For automotive technicians and car enthusiasts alike, scan tools are indispensable for diagnosing and repairing modern vehicles. These devices communicate with a car’s onboard computer system, retrieving valuable data that helps pinpoint problems. However, the information presented by scan tools often comes in the form of abbreviations, which can be perplexing if you’re not familiar with them. Understanding these abbreviations is crucial for accurate diagnosis and efficient repairs. This guide serves as your comprehensive resource to decipher the common abbreviations you’ll encounter on a scan tool, ensuring you can effectively interpret diagnostic information and get vehicles back on the road.
Common Automotive Abbreviations Explained
This section provides an extensive list of abbreviations you might find displayed on your scan tool, categorized alphabetically for easy navigation. Understanding these terms will significantly enhance your diagnostic capabilities and streamline your repair process.
4EAT – Ford Electronic Automatic 4 Speed Transaxle
This refers to a specific type of automatic transmission used by Ford, a 4-speed electronic automatic transaxle.
A – Amperes
The unit of measurement for electrical current. It indicates the rate of flow of electric charge.
A/C – Air Conditioning
Relates to the vehicle’s air conditioning system, responsible for cooling the cabin.
A/C CLUTCH SWITCH – Air Conditioning Clutch Switch
A sensor that signals the vehicle’s computer about the status of the air conditioning compressor clutch. This is important for managing engine idle speed when the A/C cycles on and off.
A/C CUT-OUT RELAY – Air Conditioning Cut-Out Relay
A relay controlled by the computer to disengage the A/C compressor clutch under heavy engine load conditions, such as wide-open throttle, to maximize engine power for acceleration.
A/C SWITCH – Air Conditioning Switch
A switch that informs the vehicle’s computer when the air conditioning system is turned on. The computer then adjusts engine idle speed to compensate for the added load of the compressor.
A/CL BIMET – Air Cleaner Bi-Metal Sensor
A temperature-sensitive sensor located in the air cleaner assembly, often used in older vehicles to control intake air temperature.
A/CL DV – Air Cleaner Duct and Valve Vacuum Motor
A vacuum-operated motor that controls a valve in the air cleaner duct to regulate the intake air temperature, drawing in either warm or cold air.
A/D – Analog to Digital Converter
An electronic circuit that converts analog signals (continuous voltage variations) into digital signals (discrete values) that can be processed by a computer.
A/F – Air Fuel Ratio
The ratio of air to fuel in the engine’s combustion mixture. Maintaining the correct A/F ratio is critical for engine efficiency, performance, and emissions control.
A/T – Automatic Transmission
Indicates components or systems related to the vehicle’s automatic transmission.
A4LD – Ford Automatic 4 Speed Lock-Up Converter Drive
Another Ford-specific automatic transmission, a 4-speed with a lock-up torque converter for improved fuel efficiency.
A4R70W – Automatic Overdrive Electronic Wide Ratio Transmission
A Ford automatic transmission, indicating an overdrive, electronically controlled, wide-ratio transmission.
AAC – Auxiliary Air Control
A system or valve that provides additional air to the engine during idle to control idle speed.
AAV – Anti-Afterburn Valve (Mazda)
A Mazda-specific valve designed to prevent afterburning in the exhaust system, reducing emissions.
ABCV – Airbleed Control Valve (Ford)
A Ford valve used to control the amount of air bled into the carburetor or intake manifold for emissions and idle control.
ABS – Antilock Brake System
The system that prevents wheel lock-up during braking, improving vehicle control and safety.
ABSV – Air Bypass Solenoid Valve (Mazda)
A Mazda solenoid valve that bypasses air in the emission control system.
ABV – Air Bypass Valve
A valve that bypasses air, often in the context of emission control or idle speed management systems.
AC – Alternating Current
An electrical current that periodically reverses direction, commonly used in vehicle charging systems and some sensors.
ACC – Air Conditioning Clutch
Refers to the clutch mechanism that engages and disengages the air conditioning compressor.
ACC – Automatic Climate Control
An advanced air conditioning system that automatically maintains a set cabin temperature.
ACCS – Air Conditioning Cycling Switch
A switch that cycles the air conditioning compressor on and off to regulate cabin temperature.
ACD – Air Conditioning Demand Switch
A switch that signals the system’s demand for air conditioning, typically activated when the driver turns on the A/C.
ACON – Air Conditioning On Signal
An electrical signal indicating that the air conditioning system is requested to be turned on.
ACP – Air Conditioning Pressure Signal
A signal from a sensor measuring the pressure within the air conditioning system.
ACPSW – Air Conditioning Pressure Switch
A switch that monitors the pressure in the air conditioning system, often used for safety and control functions.
ACR – Air Conditioning Relay
A relay that controls power to the air conditioning compressor clutch.
ACR4 – Air Conditioning Refrigerant, Recovery, Recycling, Recharging
Terms related to the process of servicing the air conditioning system, including refrigerant handling.
ACT – Air Charge Temperature sensor or signal circuit
Indicates the Air Charge Temperature sensor, which measures the temperature of the air entering the engine intake. This is crucial for fuel and ignition timing calculations.
ACTUATION TEST MODE (ATM) – Actuation Test Mode
A diagnostic mode in scan tools that allows technicians to activate and deactivate specific vehicle components (like relays, solenoids, motors) to test their functionality.
ACTUATOR – Actuator
A component that creates mechanical motion in response to an electrical, pneumatic, or hydraulic signal. Examples include motors, solenoids, and valves.
ACV – (Thermactor) Air Control Valve
Part of the Thermactor (secondary air injection) system, this valve controls the flow of air injected into the exhaust system to reduce emissions.
A-D (ANALOG-DIGITAL) CONVERTER – Analog-Digital Converter
See A/D.
ADU – Analog-Digital Unit
A module or unit containing an Analog-to-Digital Converter.
AFC – Air Flow Control
Systems or components that regulate the flow of air into the engine.
AFM – Air Flow Meter
A sensor that measures the volume or mass of air entering the engine, essential for accurate fuel delivery.
AFR – Air Fuel Ratio
See A/F.
AFS – Air Flow Sensor (Mitsubishi)
Mitsubishi’s designation for their Air Flow Sensor.
AFTER TOP DEAD CENTER – ATDC
Refers to the crankshaft position after the piston has reached its highest point in the cylinder (Top Dead Center) on the compression stroke. Used in ignition timing specifications.
AICV (AIR INJECTION CHECK VALVE) – Air Injection Check Valve
A one-way valve in the air injection system that prevents exhaust gases from flowing back into the air pump or hoses.
AIR – Secondary air injection (formerly thermactor)
Refers to the secondary air injection system, also known as Thermactor in Ford vehicles, which pumps air into the exhaust to reduce emissions.
AIR BPV – Thermactor Air Bypass Valve
A valve in the Thermactor system that bypasses secondary air injection under certain conditions.
AIR CHARGE TEMPERATURE SENSOR – Air Charge Temperature Sensor
See ACT.
AIR CLEANER VACUUM DIAPHRAGM – Air Cleaner Vacuum Diaphragm
A vacuum-operated diaphragm that controls the air intake door in the air cleaner housing, regulating the temperature of intake air.
Air Conditioning Clutch – Air Conditioning Clutch
See ACC.
AIR GAP – Air Gap
A space between two components, often in electrical or magnetic systems, such as the gap between spark plug electrodes.
AIR RELIEF VALVE (ARV) – Air Relief Valve
A valve that vents excess air pressure from the air pump in the secondary air injection system.
AIR SWITCHING/RELIEF VALVE (ASRV) – Air Switching/Relief Valve
A valve that directs secondary air injection to different points in the exhaust system depending on engine temperature and also relieves excess air pressure.
AIR/FUEL (AF) MIXTURE – Air/Fuel Mixture
See A/F.
AIRB – Air Bypass Solenoid
A solenoid valve that controls air bypass in various engine systems.
AIRD – AIR Diverter Solenoid
A solenoid that diverts air flow, often in the secondary air injection system.
AIS – Air Injection System (Chrysler)
Chrysler’s designation for their Air Injection System.
AIS – Automatic Idle Speed
Refers to systems that automatically control the engine’s idle speed.
AIS (AUTOMATIC IDLE SPEED) MOTOR – Automatic Idle Speed Motor
A motor that adjusts the idle air bypass to control engine idle speed, typically controlled by the vehicle’s computer.
AIV – Air Injection Valve
A valve that controls the injection of secondary air into the exhaust system.
ALC – Automatic Level Control
A system that automatically adjusts vehicle suspension height to maintain a level ride, regardless of load.
ALCL – Assembly Line Communications Link (GM)
GM’s early diagnostic communication protocol, predecessor to OBD-II.
ALDL – Assembly Line Data Link
Similar to ALCL, another early GM diagnostic data link.
ALT – Alternator (replaced with GEN)
The vehicle’s generator that produces electrical power to charge the battery and run electrical systems while the engine is running. Now commonly referred to as GEN (Generator).
ALTERNATING CURRENT (AC) – Alternating Current
See AC.
AM1 – Air Management 1, AIR Bypass / Thermactor Air Management (TAB)
Ford’s designation for Thermactor Air Bypass management.
AM2 – Air Management 2, AIR Diverter / Thermactor Air Management (TAD)
Ford’s designation for Thermactor Air Diverter management.
AMB – Ambient
Refers to the surrounding conditions, typically ambient temperature.
AMBIENT TEMPERATURE – Ambient Temperature
The temperature of the air surrounding an object, often measured by a sensor for climate control or engine management.
AMMETER – Ammeter
An instrument used to measure electrical current in amperes.
AMPERAGE – Amperage
The strength of an electric current, measured in amperes.
AMPERE – Ampere
See A.
AMPLIFIER – Amplifier
An electronic circuit that increases the strength of a signal (voltage or current).
AMPLITUDE – Amplitude
The maximum extent of a vibration or oscillation, in electrical terms, the peak value of a voltage signal.
ANALOG – Analog
A method of signal transmission using continuous variations in voltage or current.
ANALOG CONTROLS – Analog Controls
Control systems that use analog signals for processing and transmission.
ANALOG VOLT-OHMMETER (VOM) – Analog Volt-Ohmmeter
A traditional multimeter that uses a needle and scale to display readings of voltage, resistance, and sometimes current.
ANALOG-DIGITAL (A-D) CONVERTER – Analog-Digital Converter
See A/D.
ANTI-BFV – Anti-Backfire Valve
A valve designed to prevent backfires in the exhaust system, often used in older emission control systems.
AOD – Automatic Over Drive transmission
Ford’s Automatic Overdrive transmission, improving fuel economy at higher speeds.
AODE – Automatic Overdrive Electronic Transmission
Ford’s Automatic Overdrive Electronic transmission, electronically controlled for enhanced performance and efficiency.
AODE-W – Automatic Overdrive Electronic Wide (ratio transmission)
A variation of AODE with a wider gear ratio spread.
AP – Accelerator Pedal
The pedal that the driver uses to control engine speed and vehicle acceleration.
APC – Automatic Performance Control
A system that automatically adjusts engine parameters for optimal performance, often related to turbocharging or fuel management.
APS – Absolute Pressure Sensor (GM) / Atmospheric Pressure Sensor (Mazda)
GM and Mazda use APS to refer to sensors measuring absolute pressure, which can be Manifold Absolute Pressure (MAP) or Atmospheric Pressure (BARO).
APT – Adjustable part Throttle
Refers to systems or components that are adjustable for part-throttle operation.
ARC – Automatic Ride Control
A system that automatically controls the vehicle’s ride characteristics, often involving adjustable suspension components.
ARMATURE – Armature
The rotating part of an electric motor or generator, or the movable part of a relay or solenoid.
ARS – Automatic Restraint System
The vehicle’s system of airbags and seatbelts designed to protect occupants in a collision.
ASARC – Air Suspension Automatic Ride Control
A specific type of Automatic Ride Control that uses air suspension.
ASD – Automatic Shutdown Relay
A relay that automatically shuts down certain engine systems (fuel pump, ignition) in case of a critical fault or after an accident.
ASDM – Airbag System Diagnostic Module (Chrysler)
Chrysler’s module responsible for diagnosing and controlling the airbag system.
ASE – Automotive Service Excellence
A certification for automotive technicians, indicating a level of competency.
ASM – Acceleration Simulation Mode
A diagnostic or testing mode that simulates vehicle acceleration.
ASR – Acceleration Slip Regulation
A system that prevents wheelspin during acceleration, improving traction and stability.
ATC – Automatic Temperature Control
See ACC.
ATDC – After Top Dead Center
See AFTER TOP DEAD CENTER.
ATF – Automatic Transmission Fluid
The fluid used in automatic transmissions for lubrication, cooling, and hydraulic operation.
ATM – Actuator Test Mode
See ACTUATION TEST MODE.
ATMOSPHERIC PRESSURE – Atmospheric Pressure
The pressure exerted by the Earth’s atmosphere.
ATOMIZATION – Atomization
The process of breaking a liquid into a fine spray, crucial for fuel injection to ensure proper combustion.
ATS – Air Temperature Sensor (Chrysler)
Chrysler’s designation for their Air Temperature Sensor.
ATX – Automatic Transaxle
An automatic transmission integrated with the differential in front-wheel-drive or all-wheel-drive vehicles.
AUTOMATIC SHUT-DOWN RELAY – Automatic Shut-Down Relay
See ASD.
AVAILABLE VOLTAGE – Available Voltage
The voltage present at a specific point in a circuit, measured relative to ground.
AVOM – Analog Volt/Ohm Meter
See ANALOG VOLT-OHMMETER.
AWD – All-Wheel Drive
A drivetrain system that powers all four wheels of a vehicle.
AWG – American Wire Gage
A standard system for measuring wire diameter.
AX4S – Automatic 4-Speed Trans.
Ford’s Automatic 4-Speed Transmission.
AXOD – Automatic Overdrive transaxle
Ford’s Automatic Overdrive Transaxle.
AXOD-E – Automatic Overdrive Transaxle – Electronically Controlled
Ford’s Electronically Controlled Automatic Overdrive Transaxle.
B/MAP – Barometric/Manifold Absolute Pressure
Combined sensor or reading that considers both Barometric and Manifold Absolute Pressure.
B+ – Battery Positive Voltage
The positive voltage supplied by the vehicle’s battery.
BAC – Bypass Air Control Valve
A valve that controls bypass air, often used in idle speed control systems.
BARO – Barometric Pressure
The atmospheric pressure.
BAROMETRIC (BARO) READ SOLENOID – Barometric Read Solenoid
A solenoid used in turbocharged vehicles to provide barometric pressure readings to the computer for boost control.
BASE IDLE – Base Idle
The engine idle speed when no computer control or external factors are influencing it, set by the throttle stop screw.
BAT – Battery
The vehicle’s battery, which stores electrical energy to start the engine and power electrical systems.
BATTERY – Battery
See BAT.
BATTERY TEMPERATURE SENSOR – Battery Temperature Sensor
A sensor that measures the temperature of the battery, used in charging system control and battery management.
BATTERY VOLTAGE – Battery Voltage
The voltage potential across the terminals of the battery.
BATTERY-HOT – Battery-Hot
Describes a circuit that is directly powered by the battery, always hot (energized).
BC – Blower Control
Systems or components that control the vehicle’s blower motor for heating and air conditioning.
BCM – Body Computer Module
A computer module that controls various body-related functions in the vehicle, such as lighting, power windows, and door locks.
BEFORE TOP DEAD CENTER (BTDC) – BTDC
Refers to the crankshaft position before the piston reaches its highest point (Top Dead Center) on the compression stroke. Used for ignition timing specifications.
BHP – Brake Horsepower
A measure of engine power at the crankshaft, after losses from friction and accessories.
BHS – Bimetal Heat Sensor (Ford)
Ford’s Bimetal Heat Sensor, often used in emission control systems.
BID – Breakerless Inductive Discharge (AMC)
AMC’s Breakerless Inductive Discharge ignition system.
BIMETAL – Bimetal
Made of two different metals with different expansion rates, used in sensors and switches that react to temperature changes.
BLM – Block Learn Multiplier (replaced with LT FUEL TRIM)
GM’s Block Learn Multiplier, an early form of Long Term Fuel Trim, used to adjust fuel delivery based on long-term engine operating conditions. Now replaced by LT FUEL TRIM.
BLOWN – Blown
Describes a fuse that has melted due to excessive current, interrupting the circuit.
BMAP – Barometric/Manifold Absolute Pressure Sensor (Ford)
Ford’s Barometric/Manifold Absolute Pressure Sensor.
BOB – Breakout Box
A diagnostic tool that provides access points for testing electrical circuits without directly probing wires.
BOO – Brake On-Off input to the computer
A signal to the vehicle’s computer indicating whether the brake pedal is pressed or released.
BOOST – Boost
The pressure in the intake manifold above atmospheric pressure, created by a turbocharger or supercharger.
BP – Barometric Pressure sensor / Barometric Pressure
See BARO.
BPA – ByPass Air solenoid / Mechanical Bypass Air
Bypass Air Solenoid or Mechanical Bypass Air system.
BPCSV – Bypass Control Solenoid Valve
A solenoid valve that controls bypass functions in various systems.
BPP – Brake Pedal Position Switch
A switch that detects the position of the brake pedal, used for various systems including cruise control and transmission control.
BPS – Back Pressure Sensor
A sensor that measures back pressure, often in the exhaust system.
BPT – Back-Pressure Transducer
A transducer that measures back pressure, typically in the EGR system.
BPV – Bypass Valve (Ford)
Ford’s Bypass Valve, used in various systems.
BPW – Brake Pulse Width
The duration of brake pulses in ABS or stability control systems.
BRAKE SWITCH – Brake Switch
See BOO.
BSV – Backfire Suppressor (Ford)
Ford’s Backfire Suppressor valve, used in emission control systems.
BTDC – Before Top Dead Center
See BEFORE TOP DEAD CENTER.
BTS – Battery Temperature Sensor
See BATTERY TEMPERATURE SENSOR.
BTSI – Brake Transmission Shift Interlock
A safety mechanism that prevents shifting out of Park unless the brake pedal is pressed.
Btu – British Thermal Unit
A unit of heat energy.
BUS N – Bus Negative
The negative side of a communication bus in the vehicle’s network.
BUS P – Bus Positive
The positive side of a communication bus in the vehicle’s network.
BV – Bowl Vent Port (Ford)
Ford’s Bowl Vent Port, part of the carburetor system.
BVP – Backpressure Transducer Valve
A valve associated with a Backpressure Transducer.
BVSV – Bi-Metal Vent Control Valve
A temperature-sensitive valve that controls venting, often in emission control systems.
BVT – Backpressure Variable Transducer System (Ford)
Ford’s Backpressure Variable Transducer System.
C – Carbon / Celsius
Chemical symbol for Carbon or unit for temperature, Celsius.
C.A.R.B. – California Air Resource Board
The California state agency responsible for air pollution control and emission standards.
C3 – Computer Command Control System (GM)
GM’s early computer-controlled engine management system.
C3I – Computer Controlled Coil Ignition
GM’s ignition system that uses individual coils for each cylinder, eliminating the distributor.
C4 – Computer Controlled Catalytic Converter System (GM)
GM’s system associated with computer-controlled catalytic converters.
CAC – Charge Air Cooler
A cooler that reduces the temperature of the air charge after it’s compressed by a turbocharger, increasing air density and engine power. Also known as Intercooler.
CALIBRATION – Calibration
The process of adjusting or verifying the accuracy of a measuring instrument or system.
CANISTER – Canister
A charcoal-filled container in the evaporative emission control system that stores fuel vapors from the fuel tank.
CANISTER PURGE CONTROL VALVE (CPCV) – Canister Purge Control Valve
A valve that controls the flow of fuel vapors from the canister to the engine intake for combustion.
CANISTER PURGE SOLENOID – Canister Purge Solenoid
A solenoid valve that controls the Canister Purge Control Valve, typically activated by the vehicle’s computer.
CANP – EVAP Canister Purge Solenoid
Abbreviation for EVAPorative Emission Control system Canister Purge Solenoid.
CAPACITANCE – Capacitance
The ability of a capacitor to store an electrical charge.
CAPACITOR – Capacitor
An electronic component that stores electrical energy in an electric field.
CAPACITY – Capacity
The amount of electrical charge a battery can store, usually measured in amp-hours.
CARB – California Air Resources Board / Carburetor
See C.A.R.B. or refers to a Carburetor, a device that mixes air and fuel for combustion.
CAS – Clean Air System / Crank Angle Sensor
Can refer to Clean Air System or Crank Angle Sensor, which measures the crankshaft angle and speed.
CASE – Cranking Angle Sensing Error
A diagnostic term indicating an error with the Crank Angle Sensor during engine cranking.
CATALYTIC CONVERTER – Catalytic Converter
An emissions control device in the exhaust system that reduces harmful pollutants (hydrocarbons, carbon monoxide, and nitrogen oxides) by chemical reactions.
CBD – Closed Bowl Distributor
A type of distributor with a closed bowl design.
CC – Catalytic Converter / Climate Control / Cruise Control / Cubic Centimeters
Can refer to Catalytic Converter, Climate Control, Cruise Control, or Cubic Centimeters (a unit of volume).
CCC – COMBUSTION CONTROL COMPUTER / Computer Command Control System (GM) / Converter Clutch Control solenoid or its circuit.
See C3 or refers to the Converter Clutch Control solenoid or its circuit, which controls the torque converter lock-up clutch.
CCD – Chrysler Collision Detection / Computer Controlled Dwell
Chrysler Collision Detection system or Computer Controlled Dwell, referring to the ignition dwell time controlled by the computer.
CCD BUS – Chrysler Collision Detection BUS / Computer Controlled Dwell BUS
A communication network bus used for Chrysler Collision Detection or Computer Controlled Dwell systems.
CCDIC – Climate Control Driver Information Center
A display that provides information about the climate control system to the driver.
CCEI – Coolant Controlled Idle Enrichment (Chrysler)
Chrysler’s Coolant Controlled Idle Enrichment system.
CCEV – Coolant Controlled Engine Vacuum Switch (Chrysler)
Chrysler’s Coolant Controlled Engine Vacuum Switch.
CCM – Central Control Module / Continuous Component Monitor
Can refer to Central Control Module, a general control unit, or Continuous Component Monitor, an OBD-II function that continuously monitors certain components.
CCNT, DTC CCNT – Count Code
Diagnostic Trouble Code Count, related to the number of times a DTC has been recorded.
CCO – Converter Clutch Override
A feature or function to override the torque converter clutch operation.
CCOT – Cycling Clutch Orifice Tube
A type of orifice tube used in air conditioning systems with a cycling compressor clutch.
CCP – Climate Control Panel / Controlled Canister Purge (GM)
Can refer to the Climate Control Panel or GM’s Controlled Canister Purge system.
CCRM – Constant Control Relay Module
A module that houses and manages multiple relays for various vehicle systems.
CCS – Coast Clutch Solenoid
A solenoid that controls the coast clutch in an automatic transmission.
CCSP – Carbon Canister Storage/Purge
Refers to Carbon Canister Storage and Purge functions in the evaporative emission control system.
CCV – Canister Control Valve
A valve that controls the operation of the evaporative emission control canister.
CDCV – Canister Drain Cut Valve
A valve that cuts off canister drain, often in evaporative emission control systems.
CDI – Capacitor Discharge Ignition (AMC)
AMC’s Capacitor Discharge Ignition system.
CDR – Chrysler Diagnostic Readout
Chrysler’s early diagnostic scan tool.
CDRV – Crankcase Depression Regulator Valve
A valve that regulates crankcase depression, part of the PCV system.
CE – Commutator End
Refers to the Commutator End of an electric motor or generator.
CEAB – Cold Engine Air Bleed
Air bleed system active during cold engine operation.
CEC – Crankcase Emission Control System (Honda)
Honda’s Crankcase Emission Control system, similar to PCV systems.
CECU – Central Electronic Control Unit (Nissan)
Nissan’s Central Electronic Control Unit.
CEL – Check Engine Light
The warning light on the instrument panel that illuminates when the vehicle’s computer detects an emissions-related fault. Also known as MIL (Malfunction Indicator Lamp).
CENTRAL FUEL INJECTION – Central Fuel Injection
A type of fuel injection where one or two injectors are centrally located in the throttle body, also known as Throttle Body Injection (TBI) or Central Port Injection (CPI).
Central Fuel Injection – Central Fuel Injection
See CENTRAL FUEL INJECTION.
CER – Cold Enrichment Rod (Ford)
Ford’s Cold Enrichment Rod, part of the carburetor system for cold starts.
CES – Clutch Engage Switch
A switch that detects when the clutch is engaged.
CESS – Cold Engine Sensor Switch
A switch that senses cold engine conditions.
CFC – Chlorofluorocarbons
A type of refrigerant formerly used in air conditioning systems, now phased out due to environmental concerns.
CFI – Central Fuel Injection / Continuous Fuel Injection
Can refer to Central Fuel Injection (TBI) or Continuous Fuel Injection (CIS), a type of mechanical fuel injection.
CFM – Cubic Feet Per Minute
A unit of volume flow rate, often used to measure air flow in engines or ventilation systems.
CFV – Critical Flow Venturi
A venturi designed for critical flow conditions.
CHARGE – Charge
Describes the electrical state of a battery or capacitor, or the process of replenishing electrical energy in a battery.
CHARGE TEMPERATURE SENSOR – Charge Temperature Sensor
See ACT.
CHARGE TEMPERATURE SWITCH – Charge Temperature Switch
A temperature-sensitive switch related to charge temperature.
CHARGING VOLTAGE – Charging Voltage
The voltage produced by the alternator to charge the battery.
CHECK ENGINE LIGHT – Check Engine Light
See CEL.
CHECK VALVE – Check Valve
A one-way valve that allows flow in only one direction.
CHM – Cold Mixture Heater
A heater designed to warm the air-fuel mixture during cold starts.
CID – Cubic Inch Displacement / Cylinder Identification sensor or its circuit
Can refer to Cubic Inch Displacement (engine volume) or Cylinder Identification sensor or circuit, which identifies cylinder position for sequential fuel injection and ignition.
CIRCUIT – Circuit
A complete path for electrical current to flow.
CIRCUIT BREAKER – Circuit Breaker
A resettable protective device that interrupts current flow in a circuit in case of an overload.
CIS – Continuous Injection System (Bosch)
Bosch’s Continuous Injection System, a type of mechanical fuel injection.
CKP – Crankshaft Position Sensor
A sensor that monitors the position and speed of the crankshaft, crucial for ignition and fuel injection timing.
CKP REF – Crankshaft Position Reference
Reference signal from the Crankshaft Position Sensor.
CKT – Circuit
Abbreviation for Circuit.
CL – Closed Loop
Refers to Closed Loop operation of the engine control system, where feedback from sensors (like oxygen sensors) is used to adjust fuel and air mixture for optimal emissions and efficiency.
CLC – Converter Lockup Clutch (replaced with TCC)
Early term for Converter Lockup Clutch, now commonly referred to as TCC (Torque Converter Clutch).
CLCC – Closed Loop Carburetor Control
Carburetor control system that uses closed-loop feedback, typically from an oxygen sensor.
CLNT – Coolant
Abbreviation for Coolant, the fluid used to cool the engine.
CLOSED CIRCUIT – Closed Circuit
An electrical circuit with a complete path for current flow.
CLOSED LOOP – Closed Loop
See CL.
CLV – Calculated Load Value
A calculated value representing the engine load, used by the engine control system.
CMFI – Central Multi-port Fuel Injection
Central Multi-port Fuel Injection, a less common fuel injection type.
CMP – Camshaft Position Sensor
A sensor that monitors the position of the camshaft, used for sequential fuel injection, ignition timing, and valve timing control in some engines.
CMP REF – Camshaft Position Reference
Reference signal from the Camshaft Position Sensor.
CO – Carbon Monoxide
A colorless, odorless, poisonous gas produced by incomplete combustion, a regulated exhaust emission.
CO2 – Carbon Dioxide
A greenhouse gas produced by combustion, also a component of exhaust emissions.
COC – Conventional Oxidation Catalyst (Ford)
Ford’s Conventional Oxidation Catalyst, used to reduce hydrocarbons and carbon monoxide in exhaust.
COC (CONVENTIONAL OXIDATION CATALYST) – Conventional Oxidation Catalyst
See COC.
COMBUSTION CONTROL COMPUTER – Combustion Control Computer
An early engine control computer, primarily used in older vehicles.
COMMON POINT – Common Point
A junction or terminal where multiple circuits or components are connected.
Computer Control System – Computer Control System
A general term for a vehicle’s electronic engine management system, including sensors, actuators, and the computer itself.
COMPUTER TIMING – Computer Timing
Ignition timing controlled by the vehicle’s computer.
CONDENSER – Condenser
See CAPACITOR.
CONDUCTOR – Conductor
A material that readily conducts electricity, allowing current to flow easily.
CONNECTOR – Connector
A device used to join electrical wires or components together, allowing for easy connection and disconnection.
CONTINUITY – Continuity
A complete and uninterrupted path for electrical current flow.
CONTINUOUS SELF-TEST – Continuous Self-Test
An ongoing diagnostic test performed by the vehicle’s computer while the vehicle is operating.
CONTROLLER – Controller
A generic term for an electronic control unit or module in a vehicle, often referring to the engine control module (ECM) or powertrain control module (PCM).
Converter Clutch Override – Converter Clutch Override
See CCO.
COOLANT TEMPERATURE SENSOR (CTS) – Coolant Temperature Sensor
A sensor that measures the temperature of the engine coolant, crucial for engine management, fuel control, and cooling fan operation.
COOLANT TEMPERATURE SWITCH – Coolant Temperature Switch
A temperature-sensitive switch that activates or deactivates based on coolant temperature.
COOLANT VACUUM SWITCH COLD CLOSED (CVSCC) – Coolant Vacuum Switch Cold Closed
A coolant temperature-sensitive vacuum switch that is closed when coolant is cold.
COOLANT VACUUM SWITCH COLD OPEN (CVSCO) – Coolant Vacuum Switch Cold Open
A coolant temperature-sensitive vacuum switch that is open when coolant is cold.
COP – Coil On Plug Electronic Ignition
Ignition system where each spark plug has its own ignition coil mounted directly on top, eliminating spark plug wires.
CORE – Core
The central part of a wire or component, such as the magnetic core in a solenoid or transformer.
CP – Canister Purge (GM) / Crankshaft Position Sensor (Ford)
Can refer to Canister Purge (GM) or Crankshaft Position Sensor (Ford).
CPA – Connector Position Assurance
A feature on electrical connectors to ensure they are properly and fully connected.
CPI – Central Port Fuel Injection
See CENTRAL FUEL INJECTION.
CPP – Clutch Pedal Position
The position of the clutch pedal, detected by a sensor or switch.
CPS – Central Power Supply / Crankshaft Position Sensor
Can refer to Central Power Supply or Crankshaft Position Sensor.
CPSOV – Canister Purge Shut Off Valve (Ford)
Ford’s Canister Purge Shut Off Valve.
CPU – Central Processing Unit
The main processing unit of a computer, responsible for executing instructions.
Crankshaft Position Sensor – Crankshaft Position Sensor
See CKP.
CRK – Cranking Signal
Signal indicating the engine is cranking or starting.
CROSS-CIRCUIT SHORT – Cross-Circuit Short
A short circuit between two different circuits, causing unintended current flow.
CRT – Cathode Ray Tube
An older type of display technology, now largely replaced by LCD and LED screens.
CSC – Coolant Spark Control (Ford)
Ford’s Coolant Spark Control system.
CSE GND – PCM Case Ground
Ground connection for the Powertrain Control Module (PCM) case.
CSSA – Cold Start Spark Advance System (Ford)
Ford’s Cold Start Spark Advance System.
CSSH – Cold Start Spark Hold System (Ford)
Ford’s Cold Start Spark Hold System.
CTAV – Cold Temperature Actuated Vacuum Switch (Ford)
Ford’s Cold Temperature Actuated Vacuum Switch.
CTM – Central Timer Module
A module that manages timing functions in the vehicle’s electrical system.
CTO – Clean Tachometer Output / Coolant Temperature Override
Can refer to Clean Tachometer Output or Coolant Temperature Override.
CTOX – Continuous Trap Oxidizer
A type of catalytic converter system.
CTP – Closed Throttle Position
Indicates the throttle is in the closed position, often detected by a switch or sensor.
CTS – Charge Temperature Switch (Chrysler) / Coolant Temperature Sensor
Can refer to Charge Temperature Switch (Chrysler) or Coolant Temperature Sensor.
CTVS – Closed Throttle Vacuum Switch
A vacuum switch that is activated when the throttle is closed.
CURB IDLE – Curb Idle
The engine idle speed when the vehicle is in gear and at a standstill.
CURRENT – Current
The flow of electrical charge, measured in amperes.
CURRENT-LIMITING RESISTOR – Current-Limiting Resistor
A resistor used in a circuit to limit the amount of current flow.
CV – Constant Velocity / Control Valve
Can refer to Constant Velocity (joints in drive shafts) or Control Valve, a general term for valves used in various systems.
CVCC – Compound Vortex Controlled Combustion System (Honda)
Honda’s Compound Vortex Controlled Combustion System, an early emissions control technology.
CVR – Control Vacuum Regulator (Ford)
Ford’s Control Vacuum Regulator.
CVS – Constant Volume Sampler
Equipment used for emissions testing.
CWM-Ford – Cold Weather Modulator (Ford)
Ford’s Cold Weather Modulator.
CYCLE – Cycle
One complete repetition of a periodic process, such as an AC electrical cycle.
CYLINDER IDENTIFICATION SIGNAL (CID) – Cylinder Identification Signal
See CID.
DAB – Delayed Accessory Bus
A power bus that keeps accessories powered for a short time after the ignition is turned off.
Data Output Line to IPC – Data Output Line to Instrument Panel Cluster
Data communication line from the engine computer to the instrument panel cluster.
DATA OUTPUT LINK (DOL) – Data Output Link
See Data Output Line to IPC.
dB – Decibels
Unit of measurement for sound intensity or signal strength.
DC – Direct Current / Duty Cycle
Can refer to Direct Current (electrical current flowing in one direction) or Duty Cycle (percentage of time a signal is high or on).
DCISCA – DC Motor Idle Speed Actuator
DC Motor driven Idle Speed Actuator.
DCL – Data Communication Link
A communication link for data exchange, often referring to diagnostic communication.
DDL – Diagnostic Data Link
A specific type of Data Communication Link used for diagnostics.
DE – Drive End
The drive end of a motor or generator.
DEAD SHORT – Dead Short
A short circuit with very low resistance, causing a large current flow.
DEC – Digital Electronic Controller
Digital Electronic Controller, a type of electronic control unit.
DE-ENERGIZED – De-Energized
The state of an electrical circuit or component when power is removed.
DEFI – Digital Electronic Fuel Injection (Cadillac)
Cadillac’s Digital Electronic Fuel Injection system.
DEPS – Digital Engine Position Sensor
Digital Engine Position Sensor.
DERM – Diagnostic Energy Reserve Module and air bag (SIR) controller
Module controlling the airbag system and diagnostic functions.
DETONATION (KNOCK) SENSOR – Detonation (Knock) Sensor
A sensor that detects engine knock or detonation, allowing the computer to retard ignition timing to prevent engine damage.
DFCO – Decel Fuel Cutoff Mode
Deceleration Fuel Cutoff Mode, a fuel-saving strategy that cuts off fuel supply during deceleration.
DFI – Direct Fuel Injection
Fuel injection system where fuel is injected directly into the engine cylinders, rather than the intake manifold.
DFS – Decel Fuel Shutoff
See DFCO.
DI – Direct Ignition / Distributor Ignition (System)
Can refer to Direct Ignition (coil-on-plug or distributorless) or Distributor Ignition system.
DIAGNOSTIC MODE – Diagnostic Mode
Operating mode of the vehicle’s computer for running diagnostics and outputting diagnostic trouble codes (DTCs).
DIAGNOSTIC READ-OUT BOX (DRB) – Diagnostic Read-Out Box
Chrysler’s early scan tool, DRB.
DIAPHRAGM – Diaphragm
A flexible membrane used in vacuum and pressure actuators to convert pressure changes into mechanical motion.
DIC – Driver Information Center
Display providing information to the driver, such as fuel economy, trip data, and vehicle status.
DICM – Distributor Ignition Control Module
Module controlling a Distributor Ignition system.
DID – Driver Information Display
See DIC.
DIELECTRIC – Dielectric
An insulating material used in capacitors and other electrical components.
DIGITAL CONTROLS – Digital Controls
Control systems that use digital signals (on/off, 1/0) for processing and control.
DIGITAL INJECTION – Digital Injection
Cadillac’s brand name for Throttle Body Injection (TBI).
DIGITAL VOLT-OHMMETER (DVOM) – Digital Volt-Ohmmeter
A multimeter that displays readings digitally, typically on an LCD screen.
DIGITAL VOLT-OHMMETER (HIGH IMPEDANCE) – High Impedance Digital Volt-Ohmmeter
A DVOM with high input impedance, minimizing circuit loading during measurements, especially important for sensitive electronic circuits.
DIODE – Diode
An electronic component that allows current to flow in only one direction.
DIRECT CURRENT (DC) – Direct Current
See DC.
Direct Ignition (Waste Spark) – Direct Ignition (Waste Spark)
A type of distributorless ignition system where a spark is wasted on the exhaust stroke of one cylinder while firing the compression stroke of its paired cylinder.
DIRECT IGNITION SYSTEM (DIS) – Direct Ignition System
See DI.
DIS – Direct Ignition (Waste Spark)
See Direct Ignition (Waste Spark).
DISTANCE (SPEED) SENSOR – Distance (Speed) Sensor
See VSS (Vehicle Speed Sensor).
DISTRIBUTOR – Distributor
In older ignition systems, a rotating device that distributes high-voltage sparks to the spark plugs in the correct firing order.
DIY – Do-It-Yourself
Refers to repairs or maintenance performed by vehicle owners themselves, rather than professional mechanics.
DLC – Data Link Connector (OBD)
The standardized connector (typically 16-pin) used to connect scan tools to the vehicle’s computer for diagnostics, mandated by OBD-II standards.
DM – Drive Motor
Electric Drive Motor in electric or hybrid vehicles.
DMCM – Drive Motor Control Module
Control Module for the Drive Motor.
DMCT – Drive Motor Coolant Temperature
Temperature of the Drive Motor Coolant.
DMPI Module – Drive Motor Power Inverter Module
Power Inverter Module for the Drive Motor.
DMS – Distributor Modulator System
Distributor Modulator System.
DOHC – Dual Overhead Cam
Engine design with two camshafts in the cylinder head, typically improving valve control and engine performance.
DOL – Data Output Line to IPC
See Data Output Line to IPC.
DPC – Dynamic Pressure Control
Dynamic Pressure Control system.
DPDIS – Dual Plug Distributorless Ignition System, used on some Ford 2.3L engines
Ford’s Dual Plug Distributorless Ignition System, used on some 2.3L engines with two spark plugs per cylinder.
DPFE – Differential Pressure Feedback EGR sensor or its circuit
Differential Pressure Feedback EGR sensor, used to monitor EGR flow by measuring pressure difference across an orifice.
DPI – Dual Plug Inhibit, used on some Ford 2.3L engines
Ford’s Dual Plug Inhibit system, used on some 2.3L engines.
DRAW – Draw
The amount of electrical current consumed by a component or circuit.
DRB II – Diagnostic Readout Box (Chrysler II)
Chrysler’s upgraded scan tool, DRB II.
DRCV – Distributor Retard Control Valve
Valve controlling distributor retard, used in emission control systems.
Drive Cycle – Drive Cycle
A specific set of driving conditions and procedures required to run onboard diagnostic tests and verify repairs, especially for OBD-II systems.
DRIVER – Driver
An electronic switch, often a transistor, used to control power to a component (solenoid, relay, etc.) based on computer signals.
Driving Condition – Driving Condition
Specific operational state of the vehicle, such as idle, cruise, acceleration, cold start, etc.
DRL – Daytime Running Lights
Vehicle lights that are automatically on whenever the vehicle is running, increasing visibility.
DSO – Digital Storage Oscilloscope
An advanced electronic test instrument that displays voltage waveforms and can store them for analysis.
DSR – Ford Diagnostic Subroutine
Ford’s Diagnostic Subroutine in their engine control software.
DSS – Downshift Solenoid
Solenoid in an automatic transmission that controls downshifting.
DSSA – Dual Signal Spark Advance (Ford)
Ford’s Dual Signal Spark Advance system.
DSV – Deceleration Solenoid Valve
Solenoid Valve active during deceleration.
DTC FRZ – Diagnostic Trouble Code Freeze Frame
Diagnostic Trouble Code Freeze Frame data, which captures sensor values and engine conditions at the moment a DTC is set.
DTC(s) – Diagnostic Trouble Code(s)
Codes stored in the vehicle’s computer memory indicating a detected fault in a system or component.
DTM – Diagnostic Test Mode
See DIAGNOSTIC MODE.
DTVS – Dual Temperature Vacuum Switch
Vacuum switch that responds to two different temperature thresholds.
DUAL CATALYTIC CONVERTER – Dual Catalytic Converter
Catalytic converter system using two converters, often a close-coupled converter for quick light-off and a main converter.
DURA SPARK SYSTEM – Dura Spark System
Ford’s early electronic ignition system.
DUTY CYCLE – Duty Cycle
See DC.
DV – Delay Valve / Delay Valve, 2 Way
Delay Valve or 2-Way Delay Valve, used to slow down vacuum or pressure changes.
DV TW – Delay Valve, 2 Way
See DV.
DVAC – Distributor Vacuum Advance Control Valve
Valve controlling vacuum advance in a distributor.
DVDSV – Differential Vacuum Delay and Separator Valve
Valve combining differential vacuum delay and separation functions.
DVDV – Distributor Vacuum Delay Valve
Vacuum Delay Valve for distributor vacuum advance.
DVM (10 MEG) – Digital Voltmeter (10 Megohm impedance)
Digital Voltmeter with a minimum of 10 Megohm input impedance.
DVOM – Digital Volt-Ohmmeter
See DIGITAL VOLT-OHMMETER.
DV-TW – Relay Valve Two Way
Two-Way Relay Valve.
DVVV – Distributor Vacuum Vent Valve
Vacuum Vent Valve for distributor vacuum advance.
DWELL – Dwell
The duration in degrees of crankshaft rotation that the ignition coil primary circuit is closed, allowing it to build up magnetic field.
E4OD – Electronic 4-Speed Overdrive
Ford’s Electronic 4-Speed Overdrive automatic transmission.
EAC – Electronic Air Control (replaced with AIR)
Early Electronic Air Control system, now generally referred to as AIR (Secondary Air Injection).
EACV – Electronic Air Control Valve
Electronic Air Control Valve.
EAIR – Electronic Secondary Air Injection
Electronically controlled Secondary Air Injection.
EAS – Electronic Air Switching
Electronically controlled air switching, typically in secondary air injection systems.
EBCM – Electronic Brake Control Module
Control Module for the Electronic Brake system, often part of the ABS or stability control system.
EBP – Exhaust Back Pressure
Pressure in the exhaust system, often measured by a sensor for EGR or turbocharger control.
EBTCM – Electronic Brake T/C Module
Electronic Brake and Traction Control Module.
EC – Engine Control
General term for Engine Control systems.
ECA – Electronic Control Assembly
Ford’s term for their engine control computer in early systems.
ECC – Electronic Climate Control
See ACC.
ECCS – Electronic Concentrated Control System
Nissan’s Electronic Concentrated Control System.
ECI – Extended Compressor at Idle
Air Conditioning Compressor operation extended at idle.
ECIT – Electronic Control Ignition Timing
Electronically Controlled Ignition Timing.
ECL – Engine Coolant Level
Level of the Engine Coolant.
ECM – Engine Control Module
The main computer controlling the engine, now often referred to as PCM (Powertrain Control Module).
ECS – Emission Control System / Evaporation Control System (Chrysler)
Can refer to Emission Control System in general or Chrysler’s Evaporation Control System.
ECT – Engine Coolant Temperature sensor or circuit
Engine Coolant Temperature sensor or circuit.
ECU – Electronic Control Unit
Generic term for an electronic control module, often used interchangeably with ECM or PCM.
EDF – Electro-Drive Fan relay or its circuit
Relay or circuit for an electric cooling fan (Electro-Drive Fan).
EDIS – Electronic Direct Ignition System (replaced with EI)
Ford’s Electronic Direct Ignition System, now generally replaced by EI (Electronic Ignition).
EDM – Electronic Distributor Modulator (Ford)
Ford’s Electronic Distributor Modulator.
EEC – Electronic Engine Control (Ford)
Ford’s Electronic Engine Control system.
EEC-I, EEC-II, EEC-III, EEC-IV – Electronic Engine Control versions
Different generations of Ford’s Electronic Engine Control systems, with EEC-IV being the most widely known and used in the 1980s and 1990s.
EECS – Evaporative Emission Control System
System designed to prevent fuel vapors from escaping into the atmosphere.
EEGR – Electronic Exhaust Gas Recirculation valve (Sonic)
Electronic Exhaust Gas Recirculation valve, often a Sonic valve type.
EEGR Monitor – Electronic EGR Test
Diagnostic test or monitor for the Electronic EGR system.
EEPROM – Electronically Erasable Programmable Read Only Memory
A type of non-volatile memory that can be electronically erased and reprogrammed.
EESS – Evaporative Emission Shed System (Ford)
Ford’s Evaporative Emission Shed System.
EET – Electronic Exhaust Gas Recirculation Transducer
Electronic transducer for the EGR system.
EEVIR – Evaporator Equalized Values in Receiver
Related to air conditioning system evaporator equalization.
EFC – Electronic Feedback Carburetor (Chrysler) / Electronic Fuel Control
Can refer to Chrysler’s Electronic Feedback Carburetor or general Electronic Fuel Control systems.
EFCA – Electronic Fuel Control Assembly (Ford)
Ford’s Electronic Fuel Control Assembly.
EFE – Early Fuel Evaporation
System designed to promote early fuel evaporation, especially during cold starts, often using exhaust heat.
EFI – Electronic Fuel Injection
General term for Electronic Fuel Injection systems.
EFT – Engine Fuel Temperature
Temperature of the Engine Fuel.
EFV – Early Fuel Evaporation Valve
Valve controlling the Early Fuel Evaporation system.
EGC – Exhaust Gas Check Valve (Ford)
Ford’s Exhaust Gas Check Valve.
EGO – Exhaust Gas Oxygen Sensor (Ford)
Ford’s term for the Exhaust Gas Oxygen Sensor, now commonly referred to as O2 sensor or HO2S (Heated Oxygen Sensor).
EGOR – EGO Signal Return (Ford)
Ford’s term for the signal return circuit of the EGO sensor.
EGR – Exhaust Gas Recirculation
An emission control system that recirculates a portion of exhaust gas back into the intake manifold to reduce NOx emissions.
EGR Monitor – OBDII EGR Test
OBD-II diagnostic monitor for the EGR system.
EGR TVV – Exhaust Gas Recirculation Thermal Vacuum Valve
Thermal Vacuum Valve controlling the EGR system.
EGRB – EGR Boost Sensor
Boost sensor related to the EGR system.
EGRC – EGR Control Solenoid (Ford)
Ford’s EGR Control Solenoid.
EGRC-BPT – EGR Control Back Pressure Transducer
EGR Control system using a Back Pressure Transducer.
EGRPS – EGR Valve Position Sensor (Mazda)
Mazda’s EGR Valve Position Sensor.
EGRT – Exhaust Gas Recirculation Temperature
Temperature of the Exhaust Gas Recirculation.
EGRV – Exhaust Gas Recirculation Vent Solenoid
Vent Solenoid for the EGR system.
EGTS – Exhaust Gas Temperature Switch (replaced with EGRT)
Exhaust Gas Temperature Switch, now generally replaced by EGRT (Exhaust Gas Recirculation Temperature) sensor.
EH – Electro-Hydraulic
Systems using both electrical and hydraulic components.
EHC – Exhaust Heat Control vacuum solenoid or its circuit
Solenoid or circuit controlling Exhaust Heat Control functions, often for intake manifold heating.
EI – Integrated Electronic Ignition System
Integrated Electronic Ignition System, generally distributorless ignition systems.
EIC – Electronic Instrument Cluster
Instrument cluster using electronic displays instead of mechanical gauges.
EICV – Electronic Idle Control Valve
Electronic Idle Control Valve, used to regulate idle speed.
ELB – Electronic Lean Burn (Chrysler)
Chrysler’s Electronic Lean Burn ignition system, designed for lean air-fuel mixtures.
ELC – Electronic Level Control
See ALC.
ELCD – Evaporative Loss Control Device
Device for controlling evaporative emissions.
ELECTRIC FUEL PUMPS – Electric Fuel Pumps
Fuel pumps powered by electricity, used in most modern vehicles.
ELECTROMAGNETIC – Electromagnetic
Relating to phenomena involving electric and magnetic fields.
ELECTROMECHANICAL – Electromechanical
Devices that combine electrical and mechanical components to perform a function.
ELECTRONIC – Electronic
Relating to circuits and systems using electronic components like transistors and integrated circuits.
Electronic Control Unit – Electronic Control Unit
See ECU.
Electronic Feedback Carburetor – Electronic Feedback Carburetor
Carburetor system controlled electronically based on feedback, typically from an oxygen sensor.
ELECTRONIC FUEL CONTROL – Electronic Fuel Control
See EFC.
Electronic Fuel Injection – Electronic Fuel Injection
See EFI.
ELECTRONIC SPARK ADVANCE (ESA) – Electronic Spark Advance
Electronically controlled ignition spark advance.
ELECTRONIC SPARK CONTROL – Electronic Spark Control
Electronic system to control and adjust ignition spark timing.
ELECTRONIC SPARK CONTROL (ESC) – Electronic Spark Control
See ESC.
ELECTRONIC SPARK TIMING – Electronic Spark Timing
See EST.
EM – Engine Modification
Engine Modification, referring to changes or adjustments made to the engine.
EMB – Electromagnetic Brakes
Braking systems using electromagnetic force.
EMF – Electromotive Force (voltage)
Electromotive Force, another term for Voltage.
EMI – Electromagnetic Interference
Electrical noise or interference caused by electromagnetic fields, potentially affecting electronic circuits.
EMR – Electronic Module Retard
Electronic Module controlled Spark Retard.
EN – Generator (Alternator)
See ALT.
Enabling Criteria – Enabling Criteria
Specific conditions that must be met for an OBD-II monitor to run its diagnostic test.
ENERGIZED – Energized
State of an electrical circuit or component when power is applied.
ENGINE CONTROL MODULE – Engine Control Module
See ECM.
ENGINE CONTROL SYSTEM – Engine Control System
See Computer Control System.
ENGINE RUNNING TEST MODE – Engine Running Test Mode
Diagnostic mode where sensor values are read with the engine running.
EOBD – European On Board Diagnostics
European version of On-Board Diagnostics, similar to OBD-II.
EOP – Engine Oil Pressure
Pressure of the Engine Oil.
EOS – Exhaust Oxygen Sensor
See EGO or O2 SENSOR.
EOT – Engine Oil Temperature
Temperature of the Engine Oil.
EP – Exhaust Pressure
Pressure in the Exhaust system.
EPA – Environmental Protection Agency
US government agency responsible for environmental protection and regulations, including vehicle emissions standards.
EPC – Electronic Pressure Control
Electronic Pressure Control, often in transmissions.
EPOS – EGR Valve Position Sensor (Ford)
Ford’s EGR Valve Position Sensor.
EPROM – Erasable Programmable Read Only Memory
A type of non-volatile memory that can be erased and reprogrammed, typically using ultraviolet light.
EPT – EGR Pressure Transducer (replaced with PFE)
EGR Pressure Transducer, now often replaced by PFE (Pressure Feedback EGR) sensor.
ER – Engine running, used on some Ford system tests.
Indicates Engine Running condition in Ford diagnostic procedures.
ERS – Engine RPM Sensor
Sensor measuring Engine Revolutions Per Minute (RPM).
ESA – Electronic Spark Advance (Chrysler)
Chrysler’s Electronic Spark Advance system.
ESC – Electronic Spark Control System (Ford)
Ford’s Electronic Spark Control system.
ESD – Electrostatic Discharge
Sudden release of static electricity, which can damage sensitive electronic components.
ESS – Electronic Spark Selection (Cadillac)
Cadillac’s Electronic Spark Selection system.
EST – Electronic Spark Timing
Electronically controlled Ignition Spark Timing.
ETC – Electronic Temperature Control
See ACC.
ETP – EGR Pressure Transducer
See EPT.
ETR – Electronically Tuned Receiver
Electronically Tuned Radio Receiver.
EVAP – Evaporative Emissions System
See EECS.
EVAP CP – Evaporative Canister Purge
Evaporative Canister Purge function.
EVAP CV – Evaporative Emissions System Canister Vent
Evaporative Emissions System Canister Vent function.
EVIC – Electronic Vehicle Information Center
See DIC.
EVO – Electronic Vehicle Orifice
Electronic Variable Orifice, often in power steering systems.
EVP – EGR Valve Position sensor or its circuit
EGR Valve Position sensor or circuit.
EVR – EGR Vacuum Regulator or its circuit
EGR Vacuum Regulator or circuit.
EVRV – Electronic Vacuum Regulator Valve
Electronic Vacuum Regulator Valve.
EXH – Exhaust
Abbreviation for Exhaust system.
EXHAUST GAS OXYGEN SENSOR – Exhaust Gas Oxygen Sensor
See O2 SENSOR.
Exhaust Gas Recirculation – Exhaust Gas Recirculation
See EGR.
EXHAUST HEAT CONTROL VALVE – Exhaust Heat Control Valve
Valve that controls the flow of exhaust heat, often used to warm the intake manifold for better fuel vaporization, especially during cold starts.
F.I. – Fuel Injection
Abbreviation for Fuel Injection systems.
F4WD – Full Time Four Wheel Drive
Four-Wheel Drive system that is engaged at all times.
FAIL SAFE – Fail Safe
A backup operating mode in electronic systems that allows limited operation in case of a component failure. Also known as Limp Mode or Fail Soft.
FAN – Cooling Fan (Low or High Speed)
Refers to the engine Cooling Fan, which can operate at different speeds (Low or High) depending on cooling demand.
FAULT CODES – Fault Codes
See DTCs.
FBC – Feedback Carburetor
See Electronic Feedback Carburetor.
FBCA – Feedback Carburetor Actuator (Ford)
Ford’s Feedback Carburetor Actuator.
FC – Fan Control
Systems or components that control the cooling fan operation.
FCA – Fuel Control Assembly (Chrysler)
Chrysler’s Fuel Control Assembly.
FCS – Fuel Control Solenoid (Ford) / Feedback Control Solenoid
Can refer to Ford’s Fuel Control Solenoid or Feedback Control Solenoid, often used in carburetors.
FDBK – Feedback
General term for Feedback signals in control systems.
FDC – Fuel Deceleration Valve (Ford)
Ford’s Fuel Deceleration Valve.
FDV – Fuel Decel Valve (Ford)
See FDC.
FEED CIRCUIT – Feed Circuit
The power supply circuit or “hot” wire in an electrical system.
FEEDBACK CARBURETOR (FBC) – Feedback Carburetor
See Electronic Feedback Carburetor.
FEEDBACK CARBURETOR ACTUATOR – Feedback Carburetor Actuator
See FBCA.
FEEPROM – Flash Electronically Erasable Programmable Read Only Memory
A type of EEPROM that can be quickly erased and reprogrammed in blocks (flashed).
FEPROM – Flash Erasable Programmable Read Only Memory
See FEEPROM.
FERROMAGNETIC MATERIAL – Ferromagnetic Material
Materials that are strongly magnetized in a magnetic field, like iron and steel.
FF – Flexible Fuel
Vehicles designed to run on either gasoline or a blend of gasoline and ethanol (like E85).
FI – Fuel Injector
Abbreviation for Fuel Injector.
FIC – Fast Idle Control
Systems or components that control fast idle speed, typically during cold engine warm-up.
FICD – Fast Idle Control Device
Device used for Fast Idle Control.
Filtered Tachometer Output – Filtered Tachometer Output
A clean tachometer signal output, often used for engine control computer inputs.
FIPL – Fuel Injection Pump Lever
Fuel Injection Pump Lever sensor, often used in diesel injection systems.
FLC – Fluid Lock-up Converter (Ford)
Ford’s Fluid Lock-up Converter.
FLS – Fluid Level Sensor (GM)
GM’s Fluid Level Sensor.
FLUX LINES – Flux Lines
Lines of magnetic force in a magnetic field.
FM – Fan Motor Program in PCM
Fan Motor control program within the Powertrain Control Module (PCM).
FMEM – Failure Mode Effects Management
See FAIL SAFE.
FMVSS – Federal Motor Vehicle Safety Standards
US Federal Motor Vehicle Safety Standards.
FOM – Fix Operating Mode (Limp Mode)
See FAIL SAFE.
FP – Fuel Pump Relay (Ford) / Fuel Pump
Can refer to Ford’s Fuel Pump Relay or Fuel Pump in general.
FPM – Fuel Pump Monitor (in PCM)
Fuel Pump Monitor function within the Powertrain Control Module (PCM).
FPRC – Fuel Pump Regulator Control
Control system for the Fuel Pump Regulator.
FRC – Forced
Often indicates Forced induction, like turbocharging or supercharging.
Freeze Frame – Freeze Frame
See DTC FRZ.
FREQUENCY – Frequency
The number of cycles per second of an alternating current or signal, measured in Hertz (Hz).
FRP – Fuel Rail Pressure
Pressure of the fuel in the Fuel Rail of a fuel injection system.
FRT – Fuel Rail Temperature
Temperature of the Fuel Rail.
FRZ – Freeze Frame
See DTC FRZ.
FT – Fuel Trim
Adjustments made to the base fuel delivery rate by the engine control system to maintain the correct air-fuel ratio.
FTL – Fuel Tank Level Sensor
Sensor measuring the Fuel Tank Level.
FTO – Filtered Tachometer Output
See Filtered Tachometer Output.
FTP – Fuel Tank Pressure
Pressure within the Fuel Tank.
FTT – Fuel Tank Temperature
Temperature of the Fuel Tank.
FUEL FILTER – Fuel Filter
A filter in the fuel line to remove contaminants from the fuel.
FUEL INJECTOR – Fuel Injector
A device that sprays fuel into the engine intake manifold or cylinders.
FUEL PRESSURE (INLET) LINE – Fuel Pressure (Inlet) Line
The fuel line that delivers fuel under pressure to the engine.
FUEL PRESSURE REGULATOR – Fuel Pressure Regulator
A device that maintains a constant fuel pressure in the fuel system.
FUEL PUMP – Fuel Pump
A pump that delivers fuel from the fuel tank to the engine.
FUEL PUMP INLET SCREEN FILTER – Fuel Pump Inlet Screen Filter
A coarse filter at the fuel pump inlet to prevent large particles from entering the pump.
FUEL PUMP RELAY – Fuel Pump Relay
An electrical relay that controls power to the fuel pump.
FUEL RAIL – Fuel Rail
A manifold that distributes fuel to multiple fuel injectors in a multi-port fuel injection system.
FUEL RETURN LINE – Fuel Return Line
A fuel line that returns unused fuel from the fuel rail or throttle body back to the fuel tank.
FUEL RICH, LEAN – Fuel Rich, Lean
Descriptions of the air-fuel mixture. “Rich” means more fuel than needed, “Lean” means less fuel than needed for stoichiometric combustion.
FUEL SYSTEM INERTIA SWITCH – Fuel System Inertia Switch
A safety switch that cuts off power to the fuel pump in case of a collision.
FUEL SYSTEM TEST PORT – Fuel System Test Port
A valve or fitting in the fuel system for connecting pressure gauges or performing tests.
FUEL TANK – Fuel Tank
The container that stores the vehicle’s fuel supply.
FUEL-VACUUM SEPARATOR – Fuel-Vacuum Separator
A device to separate fuel from vacuum lines, often in older emission control systems.
FUSE – Fuse
A safety device that protects electrical circuits from overcurrent by melting a wire when current exceeds a safe level.
FUSIBLE LINK – Fusible Link
A type of fuse designed to protect high-current circuits, often used in battery and alternator circuits.
FWD – Front Wheel Drive
A drivetrain system where only the front wheels are powered.
g/sec – Grams per Second
Unit of mass flow rate, often used for air or fuel flow measurements.
GA – Gage
Abbreviation for Gage, often referring to wire gage (AWG) or pressure gage.
GCM – Governor Control Module
Control Module for a Governor system.
GCW – Gross Combination Weight
The maximum allowable combined weight of a vehicle and its trailer.
GDC – Fuel Data Center
Fuel Data Center, often part of the instrument panel or trip computer.
GDI – Gasoline Direct Injection
See DFI.
GEM – Generic Electronic Module
Ford’s Generic Electronic Module, controlling various body and accessory functions.
GEN – Generator (Alternator)
See ALT.
GENERATE – Generate
To produce electricity, typically through electromagnetic induction in an alternator or generator.
Generic Code – Generic Code
OBD-II Diagnostic Trouble Codes that are standardized across all vehicle manufacturers (P0xxx codes).
GND – Electrical Ground Connection
Electrical Ground Connection, the common reference point in a vehicle’s electrical system, typically connected to the vehicle chassis and battery negative terminal.
GOOSE – Brief Throttle Open/Close
Rapid opening and closing of the throttle.
GPM – Grams Per Mile
Unit of emissions rate, grams of pollutant emitted per mile driven.
GPS – Governor Pressure Sensor
Pressure Sensor for a Governor system, often in transmissions.
GROUND (OR GND) – Ground
See GND.
GROUND-SIDE SWITCH – Ground-Side Switch
A switch located in the ground side of a circuit, switching the ground path instead of the power path.
GST – Generic Scan Tool
A basic OBD-II scan tool that reads generic codes and data.
GVW – Gross Vehicle Weight
The maximum allowable weight of a vehicle, including its own weight, passengers, and cargo.
H – Hydrogen
Chemical symbol for Hydrogen.
H/CMPR – High Compression
High Compression engine.
H2O – Water
Chemical formula for Water.
HAC – High Altitude Compensator
System to compensate for altitude changes, often in carburetors to adjust air-fuel mixture.
HAIS – Heated Air Intake System (Chrysler)
Chrysler’s Heated Air Intake System, similar to EFE systems.
HALL EFFECT – Hall Effect
A phenomenon where a voltage is produced across a conductor carrying current when placed in a magnetic field, used in sensors like crankshaft and camshaft position sensors.
HARD FAULT – Hard Fault
A fault that is currently present and repeatable during the current engine operating cycle.
HARD FAULT CODE – Hard Fault Code
A DTC that reappears consistently after clearing codes and retesting.
HBV – Heater Blower Voltage
Voltage supplied to the Heater Blower motor.
HC – Hydrocarbons
Unburned fuel in exhaust emissions, a regulated pollutant.
HCDS – High Clutch Drum Speed
Speed of the High Clutch Drum in an automatic transmission.
HCV – Exhaust Heat Control Valve (Ford) / Hydrocarbon (Ford)
Can refer to Ford’s Exhaust Heat Control Valve or Hydrocarbon emissions (Ford’s usage).
HD – Heavy Duty
Refers to Heavy Duty components or vehicles, designed for more demanding use.
HDC – Heavy Duty Cooling
Heavy Duty Cooling system.
HDR-CKP – High Data Rate CKP Sensor
High Data Rate Crankshaft Position Sensor.
HEATED OXYGEN SENSOR (HO2S) – Heated Oxygen Sensor
An oxygen sensor with a built-in heater to bring it to operating temperature quickly and maintain it, improving closed-loop control, especially at idle and during warm-up.
Heater Blower Voltage – Heater Blower Voltage
See HBV.
HEDF – High-speed Electro-Drive Fan relay or its circuit
Relay or circuit for a High-speed Electric cooling fan.
HEGO – Heated Exhaust Gas Oxygen Sensor
See HO2S.
HEI – High Energy Ignition (GM)
GM’s High Energy Ignition system, an early electronic ignition system.
HFC – High (speed) Fan Control
High-speed Fan Control.
HFP – High Fuel Pump (Relay) Control
High Fuel Pump Relay Control.
Hg (MERCURY) – Mercury
Chemical symbol for Mercury, used as a unit of pressure measurement (inches of Mercury).
HIC – Hot-Idle Compensator (Ford)
Ford’s Hot-Idle Compensator.
HIGH TENSION SECONDARY VOLTAGE – High Tension Secondary Voltage
The high voltage generated by the ignition coil secondary winding to fire the spark plugs.
HIGH-RESISTANCE SHORT – High-Resistance Short
A short circuit with some resistance, causing a reduced but still excessive current flow.
HLOS – Hardware Limited Operation System
Hardware Limited Operation System.
HO – High Output
Refers to High Output engine or component.
HO2S – Heated Oxygen Sensor
See HEATED OXYGEN SENSOR.
HO2S-1-1, HO2S-1-2, HO2S-1-3, HO2S-2-1, HO2S-2-2 – Heated Oxygen Sensor designations
Designations for Heated Oxygen Sensors in different locations. The first number indicates the bank (1 or 2), the second number indicates the sensor position in the exhaust stream (1, 2, or 3).
hp – Horsepower
Unit of power, commonly used for engine power rating.
HPC – High Pressure Cutoff
High Pressure Cutoff switch or system.
HPL – High Pressure Liquid
High Pressure Liquid.
HPS – High Performance System
High Performance System or components.
HPV – High Pressure Vapor
High Pressure Vapor.
HSC – High Swirl Combustion
Combustion chamber design promoting high swirl of air-fuel mixture for better mixing and combustion.
HT – High Tension
Refers to High Tension voltage, typically for ignition systems.
HUD – Heads Up Display
A display that projects information onto the windshield in the driver’s line of sight.
HVAC – Heater Ventilation and Air Conditioning
Heating, Ventilation, and Air Conditioning system.
HVACM – Heater-Vent-Air Conditioning Module
Control Module for the HVAC system.
HVS – High Voltage Switch
High Voltage Switch.
Hz – Hertz
Unit of frequency, cycles per second.
I/M – Inspection and Maintenance
Vehicle Inspection and Maintenance programs for emissions control.
I/M Readiness – Inspection and Maintenance Readiness
OBD-II status indicating whether emissions-related systems have been tested and are ready for an I/M test.
I/M Test / Emissions Test / Smog Check – Inspection and Maintenance Test
See I/M Test.
I/O – Input / Output
Input and Output signals or functions in electronic systems.
I/P – Instrument Panel
Instrument Panel, the dashboard area containing gauges, displays, and controls.
IA – Intake Air
Intake Air.
IAC – Idle Air Control (motor or solenoid)
System or component for Idle Air Control, often using a motor or solenoid valve to bypass air around the throttle plate.
IACV – Idle Air Control Valve
Idle Air Control Valve, part of the IAC system.
IAS – Inlet Air Solenoid valve or its circuit
Inlet Air Solenoid valve or circuit.
IAT – Intake air temperature sensor
Intake Air Temperature sensor, measuring the temperature of the air entering the engine.
IBP – Integral Back Pressure
Integral Back Pressure system or component.
IC – Ignition Control / Integrated Circuit
Can refer to Ignition Control or Integrated Circuit (electronic component).
ICM – Ignition Control Module / Integrated Control Module
Can refer to Ignition Control Module or Integrated Control Module, a general control unit.
ICP – Injection Control Pressure
Pressure in a hydraulic injection system, often used in diesel or some gasoline direct injection systems.
ICS – Idle Control Solenoid (GM)
GM’s Idle Control Solenoid.
ID – Inside Diameter
Inside Diameter measurement.
IDI – Integrated Direct Ignition
Integrated Direct Ignition system.
IDL – Idle Position Switch
Switch that detects the Idle position of the throttle.
Idle Speed Actuator – Idle Speed Actuator
Actuator used to control engine idle speed, often a motor or solenoid.
Idle Speed Control – Idle Speed Control
See IAC.
IDLE SPEED STEPPER (ISS) MOTOR – Idle Speed Stepper Motor
Stepper Motor used for Idle Speed Control.
IDLE TRACKING SWITCH – Idle Tracking Switch
Switch that tracks the Idle position of the throttle.
IDM – Ignition Diagnostic Monitor / Injector Driver Module
Can refer to Ignition Diagnostic Monitor or Injector Driver Module, which controls fuel injectors.
IFI – Indirect Fuel Injection
Fuel injection where fuel is injected into the intake manifold, not directly into the cylinder.
IFS – Inertia Fuel Switch
See FUEL SYSTEM INERTIA SWITCH.
IGN – Ignition
Abbreviation for Ignition system.
IGN ADV – Ignition Advance
Ignition Advance, advancing the spark timing.
IGN GND – Ignition Ground
Ground connection for the Ignition system.
Ignition Diagnostic Monitor – Ignition Diagnostic Monitor
See IDM.
ILC – Idle Load Compensator
System to compensate for load changes at idle, maintaining stable idle speed.
IMA – Idle Mixture Adjuster
System to adjust the air-fuel mixture at idle.
IMPEDANCE – Impedance
The total opposition to the flow of alternating current, including resistance and reactance, measured in Ohms.
IMRC – Intake Manifold Runner Control
System to control the length or shape of intake manifold runners to optimize engine performance at different speeds.
IMS – Ignition Module Signal / Inferred Mileage Sensor (Ford)
Can refer to Ignition Module Signal or Ford’s Inferred Mileage Sensor.
IMT – Intake Manifold Tuning
See IMRC.
INDUCTION – Induction
The process of generating an electric current or magnetic field by changing a magnetic field or current.
INJ 1 to INJ 10 – Fuel Injectors 1 to 10
Designations for individual Fuel Injectors in multi-cylinder engines.
INJECTOR – Injector
See FUEL INJECTOR.
INPUTS – Inputs
Signals or data received by a computer or control module from sensors and switches.
INSULATOR – Insulator
A material that resists the flow of electricity.
INT – Integrator (replaced with ST FUEL TRIM)
Early term for Integrator in fuel control systems, now generally replaced by ST FUEL TRIM (Short Term Fuel Trim).
INTERMITTENT – Intermittent
Occurring at irregular intervals, not continuously. In electrical terms, refers to faults that come and go.
INTERMITTENT FAULT – Intermittent Fault
A fault that occurred in a previous driving cycle but is not currently present.
IPC – Instrument Panel Cluster
See I/P.
IPR – Injector Pressure Regulator
Pressure Regulator for Fuel Injectors.
IRCM – Integrated Relay Control Module
See CCRM.
ISA – Idle Speed Actuator
See Idle Speed Actuator.
ISC – Idle Speed Control
See IAC.
ISO – International Standard of Organization
International Standards Organization.
ISS – Input Shaft Speed
Speed of the Input Shaft in a transmission.
ITA – Ignition Timing Adjustment
Adjustment of Ignition Timing.
ITCS – Ignition Timing Control System (Honda)
Honda’s Ignition Timing Control System.
ITS – Idle Tracking Switch
See IDLE TRACKING SWITCH.
IVS – Idle Validation Switch
Switch to validate the Idle position of the throttle.
IVSC – Integrated Vehicle Speed Control
Integrated Vehicle Speed Control system.
IVV – Idle Vacuum Valve (Ford)
Ford’s Idle Vacuum Valve.
JAS – Jet Air System (Mitsubishi)
Mitsubishi’s Jet Air System.
JSV – Jet Mixture Solenoid Valve
Solenoid Valve for Jet Mixture control.
KAM – Keep Alive Memory
Non-volatile memory in the vehicle’s computer that retains data even when the ignition is off, used to store learned values and DTCs.
KAPWR – Keep Alive Power
Battery power supply for the KAM circuit.
KD – Kickdown
Automatic transmission Kickdown function for rapid downshifting.
KDLH – Kickdown Low Hold
Kickdown Low Hold function in an automatic transmission.
Keep Alive Memory – Keep Alive Memory
See KAM.
Kg/cm2 – Kilograms per Square Centimeter
Unit of pressure measurement.
kHz – Kilohertz
Unit of frequency, 1000 Hertz.
Km – Kilometers
Unit of distance measurement.
KNOCK SENSOR (KS) – Knock Sensor
See DETONATION (KNOCK) SENSOR.
KOEC – Key On, Engine Cranking
Diagnostic test condition: Key On, Engine Cranking (starting).
KOEO – Key On, Engine Off
Diagnostic test condition: Key On, Engine Off.
KOER – Key On, Engine Running
Diagnostic test condition: Key On, Engine Running.
KPA – Kilopascal
Unit of pressure measurement.
KS – Knock Sensor
See KNOCK SENSOR.
KSM – Knock Sensor Module
Module for the Knock Sensor system.
L – Liters
Unit of volume measurement, typically for engine displacement.
L4 – Four Cylinder Inline Engine
Inline Four-Cylinder Engine configuration.
LAB OSCILLOSCOPE – Lab Oscilloscope
See DSO.
LAMBSE – Short Term Fuel Trim
See STFT.
LCD – Liquid Crystal Display
Type of flat-panel display technology.
LEAN MIXTURE – Lean Mixture
See FUEL RICH, LEAN.
LED – Light Emitting Diode
Semiconductor light source.
LFC – Low Fan Control
Low speed Fan Control.
LFP – Low Speed Fuel Pump Control
Low Speed Fuel Pump Control.
LHD – Left Hand Drive
Vehicle configuration with steering wheel on the left side.
LIGHT-EMITTING DIODE (LED) – Light Emitting Diode
See LED.
LIMP-IN MODE – Limp-In Mode
See FAIL SAFE.
LINEAR – Linear
Relationship where a change in one variable produces a proportional change in another, represented by a straight line graph.
LOAD – Load
See CLV (Calculated Load Value).
LOC – Light Off Catalyst
Catalytic converter designed for quick light-off to reduce cold-start emissions.
LOCK UP TORQUE CONVERTER – Lock Up Torque Converter
Torque converter with a lock-up clutch that mechanically couples the engine and transmission for improved fuel efficiency.
LOCK-UP TORQUE CONVERTER SOLENOID – Lock-Up Torque Converter Solenoid
Solenoid that controls the lock-up clutch in a torque converter.
LOGIC MODULE – Logic Module
An early type of engine control computer module, often used in Chrysler vehicles.
LOGIC PROBE – Logic Probe
A test tool to check for logic levels (high/low, on/off) in digital circuits.
Long Term Fuel Trim – Long Term Fuel Trim
Fuel Trim adjustments made over a longer period to compensate for long-term engine wear or system changes.
LONGFT – Long Term Fuel Trim
See LTFT.
LOOP – Engine Operating Loop Status
Indicates whether the engine control system is in Open Loop or Closed Loop operation.
LOS – Limited Operating Strategy
See FAIL SAFE.
LPG – Liquid Petroleum Gas
Propane or Butane fuel.
LSS – Linear Shift Solenoid
Linear Shift Solenoid in an automatic transmission.
LTFT – Long Term Fuel Trim
Long Term Fuel Trim.
LTS – Low Coolant Switch
Switch that detects Low Coolant level.
LUS – Lock-Up Solenoid
Lock-Up Solenoid for torque converter lock-up.
LV8 – Load Variable
Load Variable signal or component.
LWB – Long Wheel Base
Vehicle with a Long Wheel Base.
M/C – Mixture control or mixture control solenoid
Mixture Control or Mixture Control Solenoid in a carburetor system.
M/T – Manual Transmission
Manual Transmission.
MAF – Mass Air Flow Sensor
Mass Air Flow Sensor, measuring the mass of air entering the engine.
MAF RTN – Mass Airflow Sensor Ground
Ground connection for the Mass Airflow Sensor.
MAGNETIC FIELD – Magnetic Field
The region around a magnet or current-carrying conductor where magnetic forces are present.
MAGNETIC PICK-UP COIL – Magnetic Pick-Up Coil
A type of sensor used in distributors to trigger ignition events.
MAGNETIC RELUCTANCE – Magnetic Reluctance
The opposition to magnetic flux in a magnetic circuit.
MALFUNCTION – Malfunction
A fault or failure in a system or component.
MALFUNCTION INDICATOR LIGHT (MIL) – Malfunction Indicator Light
See CEL.
MANIFOLD ABSOLUTE PRESSURE (MAP) SENSOR – Manifold Absolute Pressure Sensor
A sensor that measures the absolute pressure in the intake manifold, used to determine engine load and air density.
Manufacturer Specific Code – Manufacturer Specific Code
OBD-II Diagnostic Trouble Codes that are specific to a particular vehicle manufacturer (P1xxx or higher codes).
MAP – Manifold Absolute Pressure sensor or its circuit
See MANIFOLD ABSOLUTE PRESSURE SENSOR.
MAS – Mixture Adjust Screw
Mixture Adjust Screw on a carburetor.
Mass Air Flow Sensor – Mass Air Flow Sensor
See MAF.
MAT – Manifold Air Temperature
Manifold Air Temperature sensor, measuring air temperature in the intake manifold.
MC – Mixture Control
See M/C.
MCS – Mixture Control Solenoid (GM)
GM’s Mixture Control Solenoid.
MCT – Manifold Charge Temperature Sensor (Ford)
Ford’s Manifold Charge Temperature Sensor.
MCU – Microprocessor Control Unit (Ford)
Ford’s early engine control computer, Microprocessor Control Unit.
MCV – Manifold Control Valve (Ford)
Ford’s Manifold Control Valve.
MDP – Manifold Differential Pressure
Differential Pressure in the Intake Manifold.
MECS – Mazda Electronic Control System
Mazda Electronic Control System.
MEMCAL – Memory Calibration
Memory Calibration module, often a PROM or EEPROM containing engine calibration data.
MERCURY (Hg) – Mercury
See Hg.
MFI – Multi-port Fuel Injection
Multi-Port Fuel Injection, where each cylinder has its own fuel injector located in the intake port.
MIC – Mechanical Instrument Cluster
Instrument Cluster using mechanical gauges.
MICROPROCESSOR – Microprocessor
A small computer processor, the central processing unit of an engine control module.
MICROPROCESSOR CONTROL UNIT (MCU) – Microprocessor Control Unit
See MCU.
MIL – Malfunction Indicator Lamp
See CEL.
MISAR – Microprocessed Sensing and Automatic Regulation (GM)
GM’s Microprocessed Sensing and Automatic Regulation system.
MIXTURE CONTROL SOLENOID – Mixture Control Solenoid
See M/C.
MLP – Manual (shift) Lever Position sensor or its circuit
Manual Lever Position sensor or circuit, indicating the gear selector position in a manual transmission.
MLUS – Modulated Lock Up Solenoid or its Control Circuit (Ford)
Ford’s Modulated Lock Up Solenoid or control circuit.
MLVLPS – Manual Valve Lever Position
Manual Valve Lever Position sensor.
MODE – Mode
A specific operating state or condition of a system.
MODULE – Module
A self-contained electronic or electromechanical unit performing a specific function.
Monitor – Monitor
OBD-II diagnostic routines that test specific emissions-related systems and components.
Monitor Has/Has Not Run – Monitor Run Status
Indicates whether an OBD-II monitor has completed its diagnostic test during the current driving cycle.
MPFI – Multi-Port Fuel Injection
See MFI.
MPG – Miles Per Gallon
Unit of fuel economy, miles driven per gallon of fuel consumed.
MPH – Miles Per Hour
Unit of speed measurement.
MPI – Multi Port Injection
See MFI.
mS or ms – Millisecond
Unit of time, one-thousandth of a second.
MSFF – Miles Since First Fail
Miles driven since a DTC was first recorded.
MSLF – Miles Since Last Fail
Miles driven since a DTC was last recorded.
MST – Manifold Surface Temperature
Temperature of the Intake Manifold surface.
MT – Manual Transmission
See M/T.
MTV – Manifold Tune Valve
Valve for Intake Manifold Tuning.
MULTI-PORT FUEL INJECTION – Multi-Port Fuel Injection
See MFI.
mV or mv – Milivolt
Unit of voltage, one-thousandth of a volt.
MVLPS – Manual Valve Lever Position
See MLVLPS.
MVZ – Manifold Vacuum Zone
Vacuum zone in the Intake Manifold.
N – Nitrogen
Chemical symbol for Nitrogen.
N.C. – Normally Closed Position
Normally Closed electrical contact position, closed when de-energized.
N.O. – Normally Open Position
Normally Open electrical contact position, open when de-energized.
N/MIL – A Code Set Without a MIL Request
Diagnostic code set without triggering the Malfunction Indicator Lamp (MIL).
N/V – Input Shaft Speed to Vehicle Speed
Ratio of Input Shaft Speed to Vehicle Speed in a transmission.
NDIR – Non Dispersive Infrared
Type of sensor technology, often used in emissions analyzers.
NDS – Neutral Drive Switch
Switch that detects Neutral or Drive gear position.
NEUTRAL/SAFETY SWITCH – Neutral/Safety Switch
Switch that prevents the engine from starting unless the transmission is in Park or Neutral, also provides gear position information to the computer.
NGS – Neutral Gear Switch or its circuit
Neutral Gear Switch or circuit.
NGV – Natural Gas Vehicles
Vehicles powered by Natural Gas.
Nm – Newton Meters
Unit of torque measurement.
NON-VOLATILE MEMORY – Non-Volatile Memory
Memory that retains data even when power is removed, like EEPROM and Flash memory.
NOx – Oxides of Nitrogen
Nitrogen Oxides, a group of regulated exhaust pollutants.
NPS – Neutral Pressure Switch or its circuit
Neutral Pressure Switch or circuit in a transmission.
NTC – Negative Temperature Coefficient
Describes a component (like a thermistor) whose resistance decreases as temperature increases.
NVRAM – Non Volatile Random Access Memory
See KAM.
O2 – Oxygen
Chemical symbol for Oxygen.
O2 (OXYGEN) SENSOR – Oxygen Sensor
A sensor in the exhaust system that measures the oxygen content in the exhaust gas, used for feedback in closed-loop fuel control.
O2S-11, O2S-21 – Oxygen Sensor Signal designations
Designations for Oxygen Sensor signals. The first number indicates the bank (1 or 2), the second number indicates the sensor position (1, 2, etc.).
OASIS – Ford Motor Company Online Automotive Service Information System
Ford’s online service information system.
OBD (ON-BOARD DIAGNOSTICS) – On-Board Diagnostics
Vehicle self-diagnostic system that monitors emissions-related components and systems, detects faults, and stores diagnostic trouble codes (DTCs).
OBD 1, OBD 2 – On-Board Diagnostics versions
OBD-I is the first generation, OBD-II is the standardized second generation with enhanced capabilities.
OBD 2 Drive Cycle – OBD-II Drive Cycle
See Drive Cycle.
OBD I – On Board Diagnostics Version I
See OBD 1.
OBD II – On Board Diagnostics Version II
See OBD 2.
OBD STAT – On Board Diagnostic System Status
Status of the On-Board Diagnostic system.
OC – Oxidation Catalytic Converter
Catalytic converter that primarily reduces hydrocarbons (HC) and carbon monoxide (CO) through oxidation.
OCC – Output Circuit Check (Ford)
Ford’s Output Circuit Check diagnostic function.
OCIL – Overdrive Cancel Indicator Lamp
Indicator lamp for Overdrive Cancel function.
OCS – Overdrive Cancel Switch
Switch to cancel Overdrive function in an automatic transmission.
OCT ADJ – Octane Adjust device
Device to adjust ignition timing based on fuel octane rating.
OD – Outside Diameter / Overdrive
Can refer to Outside Diameter measurement or Overdrive gear in a transmission.
ODM – Output Device Monitor
OBD-II monitor for Output Devices (actuators).
ODS – Overdrive Drum Speed
Speed of the Overdrive Drum in an automatic transmission.
OE – Original Equipment
Original Equipment parts, manufactured by the vehicle manufacturer or their suppliers.
OEM – Original Equipment Manufacturer
Original Equipment Manufacturer, the company that manufactures the original parts for a vehicle.
OHC – Overhead Cam Engine
Engine design with the camshaft(s) located above the cylinders in the cylinder head.
OHM – Ohm
Unit of electrical resistance.
OHV – Over Head Valve
Engine design with valves located in the cylinder head and operated by pushrods from a camshaft in the engine block.
OL – Open Loop
Engine control system operating mode where it does not use feedback from sensors like oxygen sensors to adjust fuel and air mixture, typically during warm-up or under heavy load.
On-Board Computer – On-Board Computer
See ECM or PCM.
OPEN CIRCUIT – Open Circuit
An electrical circuit with a break in the path, preventing current flow.
ORC – Oxidation Reduction Converter
Catalytic converter that combines oxidation and reduction functions.
OS – Oxygen Sensor
See O2 SENSOR.
OSAC – Orifice Spark Advance Control (Chrysler)
Chrysler’s Orifice Spark Advance Control system.
OSC – Output State Check (Ford)
Ford’s Output State Check diagnostic function.
OSCILLOSCOPE – Oscilloscope
See DSO.
OSM – Output State Monitor
OBD-II monitor for Output State.
OSS – Output Speed Shaft
Speed of the Output Shaft in a transmission.
OTIS – Overhead Travel Information System
Overhead Travel Information System, often a trip computer or information display.
OVCV – Outer Vent Control Valve
Outer Vent Control Valve, often in evaporative emission control systems.
P/B – Power Brakes
Power Brakes system.
P/E – Power Enrichment
Fuel enrichment during high power demand conditions, like acceleration.
P/N – Part Number / Park Neutral Position
Can refer to Part Number or Park/Neutral position of the transmission gear selector.
P/S – Power Steering
Power Steering system.
PA – Pressure Air (Honda)
Honda’s Pressure Air system.
PAFS – Pulse Air Feeder System (Chrysler)
Chrysler’s Pulse Air Feeder System.
PAIR – Pulsed Secondary Air Injection
Pulsed Secondary Air Injection system.
PARALLEL CIRCUIT – Parallel Circuit
An electrical circuit with multiple paths for current to flow.
PAS – passive Anti-Theft System / Power Assisted Steering / Personalized Automotive Security System
Can refer to passive Anti-Theft System, Power Assisted Steering, or Personalized Automotive Security System.
PASS – Personalized Automotive Security System
See PAS.
PC – Pressure Control
Pressure Control system or component.
PCB – Printed Circuit Board
A board with conductive tracks used to connect electronic components.
PCI – Programmable Communications Interface
Programmable Communications Interface.
PCM – Powertrain Control Module
The main computer in modern vehicles that controls both engine and transmission functions, replacing separate ECM and TCM modules.
PCM (POWERTRAIN CONTROL MODULE ) – Powertrain Control Module
See PCM.
PCS – Pressure Control Solenoid
Pressure Control Solenoid, often in automatic transmissions.
PCV – Positive Crankcase Ventilation
Emission control system that vents crankcase gases back into the intake manifold to be burned in the engine.
PCV (POSITIVE CRANKCASE VENTILATION) – Positive Crankcase Ventilation
See PCV.
PECV – Power Enrichment Control Valve
Valve controlling Power Enrichment.
Pending Code – Pending Code
OBD-II Diagnostic Trouble Code that has been detected on one driving cycle but needs confirmation on a second cycle to become a confirmed DTC.
PF – Purge Flow Sensor
Sensor measuring Purge Flow in the evaporative emission control system.
PFE – Pressure Feedback EGR sensor or its circuit
Pressure Feedback EGR sensor, measuring EGR flow based on pressure feedback.
PFI – Port Fuel Injection
Port Fuel Injection, see MFI.
PFI/MFI – General abbreviation for Port or Multi-port Fuel Injection
General abbreviation for Port Fuel Injection (PFI) or Multi-Port Fuel Injection (MFI).
PGM-FI – Programmed Gas Management Fuel Injection (Honda)
Honda’s Programmed Gas Management Fuel Injection system.
PID – Parameter Identification
OBD-II Parameter Identification, refers to data parameters that can be read from the vehicle’s computer using a scan tool.
PID SUP – Parameter Identification Supported
Indicates Parameter IDs (PIDs) that are supported by the vehicle’s computer.
PIP – Profile Ignition Pickup
Ford’s Profile Ignition Pickup sensor, used for crankshaft position sensing in some ignition systems.
PIV – Peak Inverse Voltage
Peak Inverse Voltage rating of a diode.
PKE – Passive Keyless Entry
Keyless entry system that automatically unlocks the doors when the key fob is near the vehicle.
PMD – Pump Mounted Driver
Driver module mounted on a pump, often a fuel injection pump.
PNP – Par Neutral Position
Park/Neutral Position switch or sensor.
PORTED VACUUM SWITCH – Ported Vacuum Switch
Temperature-actuated vacuum switch that switches vacuum connections based on coolant temperature.
POT – Potentiometer
See POTENTIOMETER.
POTENTIOMETER (POT) – Potentiometer
A variable resistor with three terminals, used as a sensor to measure position or angle.
POWER LOSS LAMP – Power Loss Lamp
Early term for Check Engine Light on Chrysler vehicles.
POWER MODULE – Power Module
An early type of engine control computer module, often used in Chrysler vehicles, responsible for controlling actuators based on commands from the Logic Module.
Power Steering Pressure Switch – Power Steering Pressure Switch
Switch that detects pressure in the power steering system, used by the engine computer to compensate for power steering load.
POWERTRAIN CONTROL MODULE (PCM) – Powertrain Control Module
See PCM.
PPM – Parts Per Million
Unit of concentration, often used for emissions measurements.
PPS – Ported Pressure Switch (Ford)
Ford’s Ported Pressure Switch.
PR – Pressure Relief
Pressure Relief valve or system.
PRC – Pressure Regulator Control
See FPRC.
PRESSURE REGULATOR – Pressure Regulator
See FUEL PRESSURE REGULATOR.
PRIMARY WINDING – Primary Winding
The low-voltage winding of an ignition coil.
PRNDL – Park Reverse Neutral Drive Low Switch
Gear selector position switch.
PROFILE IGNITION PICKUP – Profile Ignition Pickup
See PIP.
PROM – Programmable Read Only Memory
A type of read-only memory that can be programmed once, typically containing calibration data.
PS – Power Steering
See P/S.
PSA – Pressure Switch Assembly
Pressure Switch Assembly.
PSC – Power Steering Control
Power Steering Control system.
PSI – Pounds Per Square Inch
Unit of pressure measurement.
PSOM – Programmable Speedometer Odometer Module
Programmable Speedometer Odometer Module.
PSOV – Purge Shut Off Valve (Ford)
Ford’s Purge Shut Off Valve.
PSP – Power Steering Pressure
Power Steering Pressure.
PSPS – Power Steering Pressure Switch
See Power Steering Pressure Switch.
PTC – Positive Temperature Coefficient Resistor
Resistor whose resistance increases as temperature increases.
PTO – Power Take Off (4WD Option)
Power Take Off, often for 4-Wheel Drive systems.
PTOX – Periodic Trap Oxidizer
Type of catalytic converter system.
PTU – Part Throttle Unlock
Part Throttle Unlock function, often in torque converter lock-up control.
PULSE – Pulse
A brief change in voltage or current.
PVA – Ported Vacuum Advance
Ported Vacuum Advance system for ignition timing.
PVS – Ported Vacuum Switch
Vacuum switch that is connected to ported vacuum.
PWM – Pulse Width Modulation
A technique to control power or signals by varying the width of electrical pulses.
PWR GND – Power Ground for PCM
Power Ground connection for the Powertrain Control Module (PCM).
QDM – Quad Driver Module
Module containing four Drivers (electronic switches).
QUICK TEST – Quick Test
Ford’s diagnostic Quick Test procedure for EEC-IV systems.
RABS – Rear Antilock Brake System
Antilock Brake System for the Rear wheels only.
RAM – Random Access Memory
Volatile memory that can be read from and written to, used for temporary data storage in computers.
RAP – Retained Access Power / Retained Accessory Power
System that keeps accessories powered for a short time after the ignition is turned off.
RATIO – Ratio
The proportional relationship between two quantities.
RECAL – Calibration Adjustment
Recalibration or Calibration Adjustment.
REDOX – Reduction Oxidation Converter
See ORC.
REF – Reference
Reference signal or voltage.
REFERENCE VOLTAGE (VREF) – Reference Voltage
A stable voltage supplied by the computer to some sensors as a reference point for their output signals.
RELAY – Relay
An electromechanical switch that uses a small current to control a larger current circuit.
RELIEF VALVE – Relief Valve
Valve designed to relieve excess pressure in a system.
RESISTANCE – Resistance
The opposition to the flow of electric current, measured in Ohms.
RESISTOR – Resistor
An electronic component designed to provide a specific amount of electrical resistance.
REST PRESSURE – Rest Pressure
Fuel pressure remaining in the fuel system after the engine is turned off.
RFI – Radio Frequency Interference
Electrical noise in the radio frequency range, which can interfere with electronic circuits.
RHD – Right Hand Drive
Vehicle configuration with steering wheel on the right side.
RICH MIXTURE – Rich Mixture
See FUEL RICH, LEAN.
RKE – Remote Keyless Entry
Keyless entry system operated by a remote key fob.
RM – Relay Module
See IRCM.
ROM – Read Only Memory
Non-volatile memory that contains permanent data that cannot be changed, like the vehicle’s operating software.
RON – Rated Octane Number
Fuel Octane Rating.
RPM – Revolutions Per Minute
Unit of engine speed measurement.
RRS – Variable Reluctance Sensor
Variable Reluctance Sensor, a type of electromagnetic sensor, often used for speed and position sensing.
RTD – Real Time Dampening
Real-Time Dampening suspension system.
RTN – Dedicated Sensor Ground Circuit
Dedicated Return or Ground circuit for sensors, providing a clean ground reference.
RTV – Room Temperature Vulcanizing
Type of sealant that cures at room temperature.
RVP – Reid Vapor Pressure
Measure of fuel volatility.
RWAL – Rear Wheel Anti-Lock
Rear Wheel Antilock Braking system, ABS for rear wheels only.
RWD – Rear Wheel Drive
Drivetrain system where only the rear wheels are powered.
S4WD – Selectable Four Wheel Drive
Four-Wheel Drive system that can be engaged or disengaged by the driver.
SAE – Society of Automotive Engineers / Viscosity Grade
Can refer to the Society of Automotive Engineers or SAE Viscosity Grade for oils.
SA-FV – Separator Assembly Fuel/Vacuum
Separator Assembly for Fuel and Vacuum lines.
SAVM – Spark Advance Vacuum Modulator
Vacuum Modulator for Spark Advance.
SAW – Spark Advance Word, and also Spark Angle Word
Digital word representing Spark Advance or Spark Angle in electronic control systems.
SBDS – Service Bay Diagnostic System
Ford’s Service Bay Diagnostic System.
SBEC – Single Board Engine Controller (replaced with PCM)
Chrysler’s Single Board Engine Controller, an early PCM.
SBS – Boost Solenoid (Ford)
Ford’s Boost Solenoid.
SBT – Serial Bus Traveler
Serial Bus communication protocol.
SC – Super Charged
Engine equipped with a Supercharger.
SCAP – Silicone Capacitance Absolute Pressure Sensor (Ford)
Ford’s Silicone Capacitance Absolute Pressure Sensor.
SCB – Supercharger Bypass
Supercharger Bypass valve or system.
SCC – Spark Control Computer
Early computer dedicated to Spark Control.
SCP – Standard Corporate Protocol
Ford’s Standard Corporate Protocol for diagnostic communication.
SDI – Saab Direct Ignition
Saab Direct Ignition system.
SDM – Sensing Diagnostic Module
Module that senses crash events and controls airbag deployment.
SDV – Spark Deceleration Valve / Spark Delay Valve
Can refer to Spark Deceleration Valve or Spark Delay Valve, used in early emission control systems.
SECONDARY WINDING – Secondary Winding
The high-voltage winding of an ignition coil that produces the spark voltage.
SEFI – Sequential Electronic Fuel Injection
Sequential Electronic Fuel Injection, where fuel injectors are pulsed individually in the engine’s firing order.
Self Test Input – Self Test Input
Input to the engine computer to initiate self-diagnostic tests.
Self Test Output – Self Test Output
Output from the engine computer for displaying diagnostic codes and data.
SELF-TEST – Self-Test
Onboard diagnostic self-test routines.
SENSOR – Sensor
A device that detects a physical quantity (temperature, pressure, speed, etc.) and converts it into an electrical signal.
SENSOR TEST MODE – Sensor Test Mode
Diagnostic mode to test sensor outputs.
SEO – Special Equipment Option
Special Equipment Option code.
Sequential Electronic Fuel Injection – Sequential Electronic Fuel Injection
See SEFI.
Sequential Fuel Injection – Sequential Fuel Injection
See SEFI.
SERIES CIRCUIT – Series Circuit
An electrical circuit with only one path for current flow, components are connected end-to-end.
SERVICE REMINDER INDICATOR (SRI) – Service Reminder Indicator
A light or message that indicates the vehicle is due for scheduled service.
SES – Service Engine Soon (replaced with MIL)
Early term for Check Engine Light, now generally replaced by MIL (Malfunction Indicator Lamp).
SFI – Sequential Fuel Injection
See SEFI.
SHED – Sealed Housing Evaporative Determination System
Test procedure for evaporative emissions.
Shift Indicator Lamp – Shift Indicator Lamp
Lamp that indicates the optimal time to shift gears for fuel economy.
SHO – Super High Output Engine
Super High Output engine variant.
SHORT – Short Circuit
An unintended low-resistance path in an electrical circuit, causing excessive current flow.
SHRT FT – Short Term Fuel Trim
Short Term Fuel Trim, immediate adjustments to fuel delivery to maintain the correct air-fuel ratio.
SHRTFT1 – Short Term Fuel Trim Bank 1
Short Term Fuel Trim specifically for engine Bank 1.
SIG RTN – Signal Return (sensor ground)
Signal Return circuit, often used as a dedicated ground for sensors.
SIL – Shift Indicator Lamp
See Shift Indicator Lamp.
SINGLE BOARD ENGINE CONTROLLER – Single Board Engine Controller
See SBEC.
SINGLE MODULE ENGINE CONTROLLER (SMEC) – Single Module Engine Controller
See SMEC.
SIPS – Side Impact Protections System
Side Impact Protection System.
SIR – Supplemental Inflatable Restraint (SIR) system; air bag
Supplemental Inflatable Restraint system, Airbag system.
SIS – Solenoid Idle Stop
Solenoid-operated Idle Stop system.
SMEC – Single Module Engine Controller (replaced with PCM)
Chrysler’s Single Module Engine Controller, an early PCM.
SMPI – Sequential Multiport Fuel Injection (Chrysler)
Chrysler’s Sequential Multiport Fuel Injection system.
SO2 – Sulfur Dioxide
Sulfur Dioxide, a component of exhaust emissions.
SOFT FAULT CODE – Soft Fault Code
A DTC that was recorded but does not reappear after clearing codes and retesting.
SOHC – Single Overhead Cam
Engine design with one camshaft in the cylinder head.
SOLENOID – Solenoid
An electromechanical device that uses an electromagnetic coil to move a plunger or valve.
SOLID STATE – Solid State
Electronic circuits using transistors, diodes, and integrated circuits, without vacuum tubes.
SPARK ADVANCE – Spark Advance
Igniting the air-fuel mixture earlier in the compression stroke.
Spark Output Signal – Spark Output Signal
Signal from the engine computer to the ignition module to trigger spark events.
SPARK RETARD – Spark Retard
Igniting the air-fuel mixture later in the compression stroke.
SPARK RETARD SOLENOID – Spark Retard Solenoid
Solenoid used to retard ignition timing, often for knock control.
SPD – Speed
Speed, often referring to vehicle speed or engine speed.
SPEED (DISTANCE SENSOR) – Speed (Distance) Sensor
See VSS.
SPFI – Single Point Fuel Injection (throttle body)
Single Point Fuel Injection, see CENTRAL FUEL INJECTION.
SPI – Serial Peripheral Interface
Serial communication protocol for peripheral devices.
SPL – Smoke Puff Limiter
System to limit smoke puffing in diesel engines.
SPOUT – Spark Output Signal
Ford’s Spark Output signal.
SPS – Service Programming System
System for reprogramming vehicle control modules.
SRC – Selective Ride Control
Selective Ride Control suspension system.
SRDV – Spark Retard Delay Valve
Valve to delay Spark Retard action.
SRI – Service Reminder Indicator
See SERVICE REMINDER INDICATOR.
SRS – Spark Retard Solenoid / Supplemental Restraint System (air bag)
Can refer to Spark Retard Solenoid or Supplemental Restraint System (Airbag system).
SRT – System Readiness Test
Diagnostic test to check system readiness.
SS – Speed Sensor (Honda)
Honda’s Speed Sensor.
SS1, SS2,etc. – Shift Solenoid 1, 2, etc.
Designations for Shift Solenoids in automatic transmissions.
SSI – Solid State Ignition system
Solid State Ignition system.
ST – Scan Tool
Abbreviation for Scan Tool, diagnostic tool used to communicate with vehicle computers.
STAR – Self Test Automatic Readout
Ford’s Self Test Automatic Readout system.
STFT – Short Term Fuel Trim
See SHRT FT.
STI – Self Test Input
See Self Test Input.
STO – Self Test Output
See Self Test Output.
STOICHIOMETRY – Stoichiometry
The ideal air-fuel ratio for complete combustion, typically around 14.7:1 for gasoline engines.
STS – Service Throttle System (lamp)
Service Throttle System warning lamp.
SUSP – Suspension System Module
Control Module for the Suspension system.
SVV – Solenoid Vent Valve (Ford)
Ford’s Solenoid Vent Valve.
SWB – Short Wheel Base
Vehicle with a Short Wheel Base.
T.V. – Throttle Valve
Throttle Valve.
TA – Temperature Air (Honda)
Honda’s Temperature Air sensor.
TAB – Thermactor Air Bypass
Thermactor Air Bypass system.
TAC – Thermostatic Air Cleaner (GM) / Throttle Actuator Control
Can refer to GM’s Thermostatic Air Cleaner or Throttle Actuator Control system.
TACH – Tachometer
Instrument that measures and displays engine speed (RPM).
TACH INPUT – Tachometer Input
Engine speed signal input to the computer, often from the ignition system.
TAD – Thermactor Air Diverter solenoid
Thermactor Air Diverter solenoid.
TAP – Transmission Adaptive Pressure
Transmission Adaptive Pressure control.
TAV – Temperature Actuated Vacuum
Temperature Actuated Vacuum system or component.
TBI – Throttle Body Injection
See CENTRAL FUEL INJECTION.
TC – Turbocharger / Torque Converter
Can refer to Turbocharger or Torque Converter.
TCA – Thermostat Controlled Air Cleaner
See TAC.
TCC – Torque Converter Clutch
Clutch that locks up the torque converter for direct mechanical coupling.
TCCP – Torque Converter Clutch Pressure
Hydraulic pressure controlling the Torque Converter Clutch.
TCCS – Toyota Computer Controlled System
Toyota Computer Controlled System.
TCIL – Transmission Control Indicator Lamp
Warning lamp for the Transmission Control system.
TCM – Transmission Control Module
Computer module that controls the automatic transmission.
TCP – Temperature Compensated Accelerator Pump (Ford) / Torque Charger / Temperature Compensating Pump
Can refer to Ford’s Temperature Compensated Accelerator Pump, Torque Charger, or Temperature Compensating Pump.
TCS – Traction Control Switch / Transmission Control Switch / Transmission Controlled Spark (GM)
Can refer to Traction Control Switch, Transmission Control Switch, or GM’s Transmission Controlled Spark system.
TD – Turbo Diesel
Turbocharged Diesel engine.
TDC – Top Dead Center
The highest point the piston reaches in the cylinder on the compression stroke.
TDI – Turbo Direct Injection
Turbocharged Direct Injection engine, typically diesel.
TE – Thermal Expansion
Thermal Expansion.
TFI – Thick Film Ignition module
Ford’s Thick Film Ignition module, an ignition control module.
TFP – Throttle Fluid Pressure / Transmission Fluid Pressure
Can refer to Throttle Fluid Pressure or Transmission Fluid Pressure.
TFT – Transmission Fluid Temperature
Temperature of the Transmission Fluid.
THERMACTOR AIR BYPASS SOLENOID – Thermactor Air Bypass Solenoid
Solenoid controlling Thermactor Air Bypass.
THERMACTOR AIR CONTROL VALVE – Thermactor Air Control Valve
Valve controlling Thermactor Air injection.
THERMACTOR AIR DIVERTER SOLENOID – Thermactor Air Diverter Solenoid
Solenoid controlling Thermactor Air Diverter valve.
THERMACTOR AIR SYSTEM – Thermactor Air System
Ford’s Secondary Air Injection system.
THERMISTOR – Thermistor
A temperature-sensitive resistor whose resistance changes with temperature.
THM – Turbo Hydra-Matic
GM’s Turbo Hydra-Matic automatic transmission series.
THREE-WAY CATALYST – Three-Way Catalyst
Catalytic converter that reduces all three main pollutants: hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx).
THROTTLE POSITION SENSOR (TPS) – Throttle Position Sensor
A sensor that measures the position of the throttle plate, providing input to the computer about driver throttle demand.
TI – Transistorized Ignition System
Transistorized Ignition system.
TIC – Thermal Ignition Control (Chrysler)
Chrysler’s Thermal Ignition Control system.
TIMING – Timing
Refers to ignition timing, valve timing, or cam timing, the precise synchronization of engine events.
TIV – Thermactor Idle Vacuum Valve (Ford)
Ford’s Thermactor Idle Vacuum Valve.
TK – Throttle Kicker Actuator (Ford) / Throttle Kicker solenoid
Can refer to Ford’s Throttle Kicker Actuator or Throttle Kicker Solenoid, used for idle speed control.
TKS – Throttle Kicker Solenoid
See TK.
TOT – Transmission Oil Temperature
Temperature of the Transmission Oil.
TP – Throttle Position sensor or its circuit / Throttle Position
Can refer to Throttle Position sensor or circuit, or Throttle Position itself.
TP Mode – Throttle Position Mode
Throttle Position Mode.
TPCV – Tank Pressure Control Valve
Valve for Tank Pressure Control, often in evaporative emission control systems.
TPI – Tuned Port Injection
Type of Multi-Port Fuel Injection with tuned intake runners for performance.
TPM – Tire Pressure Monitor
Tire Pressure Monitoring system.
TPP – Throttle Position Potentiometer
Throttle Position Potentiometer, another term for TPS.
TPS – Throttle Position Sensor
See THROTTLE POSITION SENSOR.
TPT – Throttle Position Transducer (Chrysler)
Chrysler’s Throttle Position Transducer.
TR – Transmission Range Sensor
Sensor that indicates the selected gear range of an automatic transmission.
TRANSDUCER – Transducer
A device that converts energy from one form to another, often converting a physical quantity into an electrical signal.
Trip – Trip
A single driving event from engine start to engine shutdown.
Trip Drive Cycle – Trip Drive Cycle
See Drive Cycle.
TRLHP – Thermal Vacuum Valve
Thermal Vacuum Valve.
TRS, TRS+1 – Transmission Regulated Spark Control System
Transmission Regulated Spark Control system.
TSB – Technical Service Bulletin
Technical Service Bulletin, information from vehicle manufacturers to technicians about common problems and repair procedures.
TSP – Throttle Solenoid Positioner (Ford)
Ford’s Throttle Solenoid Positioner.
TSS – Transmission Shaft Speed Sensor / Turbine Speed Shaft Sensor
Can refer to Transmission Shaft Speed Sensor or Turbine Speed Shaft Sensor in an automatic transmission.
TTS – Transmission Temperature Switch
Switch that detects Transmission Temperature.
Tuned Port Injection – Tuned Port Injection
See TPI.
TV – Throttle Valve
See T.V.
TVS – Temperature Vacuum Switch
Temperature-sensitive Vacuum Switch.
TVV – Thermal Vent Valve (Ford)
Ford’s Thermal Vent Valve.
TWC – Three Way Catalyst / Three-Way Catalyst
See THREE-WAY CATALYST.
TWC + OC – Three Way Catalyst + Oxidation Catalyst
Catalytic converter system combining a Three-Way Catalyst and an Oxidation Catalyst.
UART – Universal Asynchronous Receiver-Transmitter
Communication protocol for serial data transmission.
UD – Underdrive
Underdrive gear or system, often in transmissions.
UIDI – Up-Integrated Direct Ignition
Up-Integrated Direct Ignition system.
UP-SHIFT LIGHT – Up-Shift Light
Indicator light that signals the driver to shift to a higher gear for fuel economy.
V – Volts
Unit of electrical potential or voltage.
VAC – Vacuum
Pressure below atmospheric pressure.
VACUUM – Vacuum
See VAC.
VACUUM ADVANCE – Vacuum Advance
Ignition timing advance controlled by intake manifold vacuum.
VACUUM CHECK VALVE (VCV) – Vacuum Check Valve
One-way valve that allows vacuum to pass in one direction but blocks it in the opposite direction.
VACUUM REGULATOR – Vacuum Regulator
Device to regulate vacuum pressure.
VACUUM REGULATOR/SOLENOID – Vacuum Regulator/Solenoid
Combined Vacuum Regulator and Solenoid valve.
VACUUM RETARD DELAY VALVE (VRDV) – Vacuum Retard Delay Valve
Valve that delays the application of vacuum retard.
VAF – Vane Air-Flow sensor or its circuit / Volume Air Flow
Can refer to Vane Air-Flow sensor or circuit, or Volume Air Flow measurement.
VAT – Vane Air Temperature Sensor / Vane Air-Flow Temperature sensor
Vane Air Temperature sensor.
VATS – Vehicle AntiTheft System
Vehicle Anti-Theft System.
VBAT – Vehicle (system) Battery Voltage
Vehicle Battery Voltage.
VCC – Vacuum Cut Control Solenoid
Vacuum Cut Control Solenoid.
VCM – Vehicle Control Module
General term for Vehicle Control Module, a central control unit in some vehicles.
VCRM – Variable Control Relay Module
Variable Control Relay Module.
VCTS – Vacuum Control Temperature Sensing Valve (Ford)
Ford’s Vacuum Control Temperature Sensing Valve.
VCV – Vacuum Control Valve (Ford) / Vacuum Check Valve
Can refer to Ford’s Vacuum Control Valve or Vacuum Check Valve.
VDOT – Variable Displacement Orifice Tube
Variable Displacement Orifice Tube in air conditioning systems.
VDV – Vacuum Delay Valve / Vacuum Differential Valve (Ford)
Can refer to Vacuum Delay Valve or Ford’s Vacuum Differential Valve.
VECI – Vehicle Emission Control Information Decal
Decal located in the engine compartment with vehicle-specific emission control information and settings.
VEHICLE EMISSION CONTROL INFORMATION (VECI) – Vehicle Emission Control Information
See VECI.
VF – Vacuum Fluorescent
Vacuum Fluorescent display technology.
VIM – Vehicle Interface Module
Vehicle Interface Module.
VIN – Vehicle Identification Number
Unique serial number identifying a vehicle.
VIS – Variable Induction System
Variable Induction System, see IMRC.
VLCM – Variable Load Control Module
Variable Load Control Module.
VM – Vane Meter or air flow meter
Vane Meter Air Flow sensor.
VMV – Vacuum Modulator Valve / Vapor Management Valve (EVAP)
Can refer to Vacuum Modulator Valve or Vapor Management Valve in the EVAP system.
VNT – Variable Nozzle Turbocharger
Turbocharger with Variable Nozzle Turbine, allowing for variable boost control.
VOLTAGE – Voltage
Electrical potential difference, the driving force that causes current to flow, measured in Volts.
VOLUMETRIC EFFICIENCY – Volumetric Efficiency
The ratio of the actual amount of air drawn into the engine cylinder to the theoretical maximum volume.
VOTM – Vacuum Operated Throttle Modulator (Ford)
Ford’s Vacuum Operated Throttle Modulator.
VPWM – Variable Pulse Width Modulated
Variable Pulse Width Modulation, a control technique.
VPWR – Ignition Switched Power
Power supply that is switched on and off with the ignition key.
VR – Voltage Regulator
Device that regulates and maintains a constant voltage level.
VR/S – Vacuum Regulator/Solenoid (Ford)
See VACUUM REGULATOR/SOLENOID.
VRDV – Vacuum Retard Delay Valve (Ford)
See VACUUM RETARD DELAY VALVE.
VREF – Reference Voltage (from PCM)
See REFERENCE VOLTAGE.
VRESER – Vacuum Reservoir (Ford)
Ford’s Vacuum Reservoir.
VREST – Vacuum Restrictor (Ford)
Ford’s Vacuum Restrictor.
VRIS – Variable Resonance Induction System
See IMRC.
VRS – Variable Reluctance Sensor
See RRS.
VRV – Vacuum Regulator Valve (Ford)
Ford’s Vacuum Regulator Valve.
VSS – Vehicle Speed Sensor
Sensor that measures vehicle speed, often located in the transmission or wheel hub.
VVA – Venturi Vacuum Amplifier (Ford)
Ford’s Venturi Vacuum Amplifier.
VVC – Variable Voltage Choke (Ford)
Ford’s Variable Voltage Choke system.
VVV – Vacuum Vent Valve (Ford)
Ford’s Vacuum Vent Valve.
W/B – Wheelbase
Vehicle Wheelbase measurement.
WAC – WOT A/C Cutout Relay
Wide Open Throttle Air Conditioning Cutout Relay.
WACA – A/C WOT Cutout Relay Monitor
Air Conditioning Wide Open Throttle Cutout Relay Monitor.
Warm-up Cycle – Warm-up Cycle
Engine operation cycle required to reach operating temperature from a cold start.
WASTEGATE CONTROL SOLENOID – Wastegate Control Solenoid
Solenoid that controls the wastegate valve on a turbocharger to regulate boost pressure.
WOT – Wide Open Throttle or Wide Open Throttle switch / Wide Open Throttle
Can refer to Wide Open Throttle condition or Wide Open Throttle switch.
WOTV – Wide-Open Throttle Valve (Ford)
Ford’s Wide-Open Throttle Valve.
WSS – Wheel Speed Sensor
Sensor that measures wheel speed, used in ABS and stability control systems.
WU OC – Warm Up Oxidation Catalytic Converter
Warm-Up Oxidation Catalytic Converter, designed for quick light-off during cold starts.
WU TWC – Warm Up Three Way Catalytic Converter
Warm-Up Three-Way Catalytic Converter, designed for quick light-off during cold starts.
ZONED VACUUM SWITCHES – Zoned Vacuum Switches
Vacuum switches used in zones or groups, often in older Ford systems.
This comprehensive glossary should significantly aid anyone working with automotive scan tools in understanding the abbreviations they encounter. By demystifying these terms, technicians and enthusiasts can more effectively diagnose vehicle issues and ensure accurate repairs.
