Are you truly maximizing the potential of your scan tool? Many automotive technicians use scan tools primarily for retrieving Diagnostic Trouble Codes (DTCs) and examining parameter data. However, they often overlook other robust features that can significantly enhance diagnostic capabilities. One of these frequently underutilized features is bidirectional control, a capability present in most enhanced scan tools. Understanding and effectively using bidirectional control, often facilitated by a Bidirectional Function Scan Tool, can revolutionize your diagnostic approach.
Bidirectional control, in essence, refers to the two-way communication between a diagnostic device, like a scan tool, and a vehicle’s control modules. Vehicle manufacturers design their computer control systems to allow a scan tool to not only request information but also to command modules to perform specific tests and functions. Manufacturers may use various terms for bidirectional controls such as functional tests, actuator tests, inspection tests, or system tests. Even advanced procedures like reinitialization and reprogramming fall under the umbrella of bidirectional control.
This article aims to explore the advantages and limitations of bidirectional controls and to demonstrate their practical application in the diagnostic process. While specific scan tools will be mentioned for illustrative purposes, this is not an exhaustive evaluation of every tool available. The focus is on empowering you to leverage the power of bidirectional function scan tools in your daily diagnostics.
The scan tool itself, particularly when equipped with bidirectional capabilities, can rightfully be called a bidirectional tool. It operates by sending requests to and receiving responses from the vehicle’s control modules. For example, in basic OBD II Mode 1, when you request parameter data, your scan tool initiates a request to the Powertrain Control Module (PCM), and the PCM responds by sending the requested data back for display. However, advanced bidirectional function scan tools go far beyond basic data retrieval. They empower technicians to actuate components like relays, injectors, and coils, and to execute comprehensive system tests, directly from the tool.
Alt text: Bidirectional control options on a Honda Civic using Teradyne Pocket Tester scan tool, showing Inspection Menu with functional tests like fuel pump and AC clutch control.
Figure 1 illustrates screen captures from a 2004 Honda Civic, utilizing the Teradyne Pocket Tester. Notice the “Inspection Menu” which houses the bidirectional controls for this vehicle. As you can see, a range of valuable tests are readily accessible. A technician can command the fuel pump to turn on or off, cycle the air conditioning clutch, and even initiate an evaporative emissions leak test. The breadth of available options is determined by both the vehicle’s programming and the scan tool’s capabilities.
This raises a crucial question: Are all scan tools created equal when it comes to bidirectional functionality? The answer is definitively no. Designing and manufacturing scan tools is a complex undertaking for both vehicle manufacturers (OEMs) and aftermarket companies. Automakers invest significant resources in developing diagnostic tools tailored to their specific vehicle lines. While cost is a factor, their primary goal is to create a comprehensive diagnostic platform capable of communicating with and diagnosing all vehicle systems. They cannot afford to omit essential functionalities.
Aftermarket scan tool manufacturers, conversely, operate with a different set of considerations. While they benefit from understanding the capabilities of factory scan tools, they face unique challenges that OEMs do not. Regarding bidirectional function scan tools, two key issues stand out:
Information Availability and Complexity: Is the necessary design information for implementing bidirectional controls readily available from vehicle manufacturers for aftermarket tool development? If OEMs make this information accessible, it simplifies the process for aftermarket manufacturers. However, even with available information, implementing bidirectional controls remains a complex and costly endeavor. Liability and safety concerns further complicate the process. For instance, commanding an engine speed increase while the transmission is in gear and the brake is not applied could lead to vehicle damage or personal injury. Protective measures must be implemented, either within the vehicle module itself or designed into the scan tool. Aftermarket manufacturers need to thoroughly understand these safety protocols.
Cost Considerations and Feature Sets: What are shop owners and technicians willing to invest in an aftermarket scan tool? Each scan tool manufacturer must carefully evaluate the development costs and prioritize features that are most valuable to technicians. Historically, engine control systems were the primary focus of vehicle computerization, leading to an emphasis on engine diagnostics in scan tool development. Even with this focus, many aftermarket scan tools still lack the full range of parameters and tests available in factory scan tools. Many shop owners and technicians opt for factory scan tools to ensure complete diagnostic coverage. This is becoming increasingly critical as non-engine control systems like Anti-lock Braking Systems (ABS), Supplemental Restraint Systems (SRS), climate control, electronic transmissions, and body control systems become more sophisticated. To remain competitive, aftermarket bidirectional function scan tool manufacturers must continually expand the system coverage and depth of functionality in their equipment.
Despite these challenges, aftermarket scan tool manufacturers have made significant strides in delivering robust bidirectional function scan tools. However, it’s important to recognize that factory scan tools may still offer certain tests or features not found in aftermarket tools. Each type of tool is designed for a different market and caters to distinct objectives and needs.
Getting Down to Diagnostics with Bidirectional Control
When used effectively, bidirectional component and system tests offered by a bidirectional function scan tool can dramatically reduce diagnostic time. Consider a no-start scenario. You’ve checked fuel pressure manually and found none. At this point, the issue could stem from a component failure, a circuit problem, or a command malfunction. If your scan tool offers a fuel pump command function, utilize it. Command the fuel pump to turn on using your bidirectional function scan tool. If fuel pressure now registers, you’ve confirmed the fuel pump and its circuit are functioning correctly.
Your diagnostic focus can then shift to the command side of the circuit. The PCM might be lacking the necessary enabling criteria to activate the fuel pump, perhaps due to a faulty input sensor like a low oil pressure sensor. This entire process, leveraging the bidirectional function scan tool, can take less than five minutes. Manually testing the fuel pump circuit, in contrast, would likely consume significantly more time.
Another example involves a Honda Civic with an illuminated Malfunction Indicator Light (MIL) and a DTC P1404 (EGR Stuck Closed). The next step is to determine if the problem is current or intermittent.
Alt text: EGR system test using bidirectional controls on Teradyne Pocket Tester, showing test initiation, RPM instructions, EGR lift sensor data, and test results indicating normal system operation.
Figure 2 displays screen captures from the Teradyne Pocket Tester during an EGR test. Box 1 highlights the “EGR Test” within the Inspection Menu. The red-circled information box to the right (Box 2) provides crucial details about the test. Box 3 shows the test initiation, and Box 4 instructs the technician to increase engine speed to 2500-3000 RPM. Box 5 showcases live data, including the EGR Lift Sensor bar graph, indicating EGR valve function. Box 6 displays the test result: “System Normal.” If intermittency is suspected, repeating this test with your bidirectional function scan tool can help confirm a sticking EGR valve. A failed test would then warrant further investigation and potential EGR valve replacement.
Recently, a 1995 Dodge Stratus with an MIL and DTC P0443 (Evap Purge Solenoid Circuit) came into the shop. Diagnostic information revealed that the factory DRB III scan tool could command the purge solenoid open and closed. Aftermarket bidirectional function scan tools like the Vetronix Mastertech and Snap-on Scanner also offer this capability.
Alt text: Evap Purge Solenoid Test using Vetronix Mastertech 3100 bidirectional scan tool, showing purge test options, vacuum line inspection suggestion, purge solenoid control instructions, initial and changed fuel trim values during the test.
Figure 3 shows Vetronix Mastertech 3100 screen captures. Box 1 shows the “F6: Purge Test” option. Box 2 offers the choice to block or permit purge flow; “F1: Flow” is selected. Box 3 smartly suggests a visual inspection of vacuum lines, highlighting the importance of preliminary checks. Box 4 explains scan tool arrow key control of the purge solenoid. Box 5 displays initial Long Term Adaptive Fuel Trim values.
When the purge valve is commanded open using the bidirectional function scan tool, fuel trim values are expected to change based on fuel vapor concentration in the tank. Rich vapor concentration should decrease fuel trim, while lean (high oxygen) concentration should increase it. Box 6 shows the purge valve commanded on. Initially, no fuel trim change occurred, suggesting a sticking purge solenoid. Cycling the valve on and off several times with the bidirectional function scan tool eventually resulted in increased fuel trim levels, indicating the solenoid finally opened. This confirmed the need for purge solenoid replacement.
Another case involved a 2004 Toyota Camry with illuminated SRS and Passenger Air Bag lights, referred by a body shop after accident repairs. A Mastertech with Toyota software was needed to access the SRS system. For many shops without specialized equipment, SRS diagnostics can be challenging. Using the Mastertech bidirectional function scan tool, DTC B1782 (Occupant Classification Sensor Rear LH Circuit Malfunction) was retrieved. Visual inspection revealed a disconnected Rear LH sensor connector.
Alt text: Mastertech bidirectional scan tool screens showing Toyota SRS controller options, sensor data display, and occupant classification sensor readings before calibration.
Figures 4-6 illustrate Mastertech screens. Figure 4, Box 2 shows controller options. After reconnecting the sensor, sensor data was checked (Box 3). Box 4 displays sensor readings, ranging from 5.50 to 6.60 lbs. The diagnostic procedure recommended Zero Calibration after seat replacement.
Alt text: Mastertech bidirectional scan tool screens showing Zero Calibration procedure for Toyota occupant classification sensor, including instructions and completion confirmation.
Figure 5 shows Zero Calibration screens (Box 1). Boxes 2 and 3 provide test preparation instructions. Box 4 confirms “Zero Calibration Complete” and suggests a Sensitivity Check.
Alt text: Mastertech bidirectional scan tool screens showing Sensitivity Check procedure for Toyota occupant classification sensor, including weight application instructions, sensor readings at 0 lbs and 66 lbs, confirming sensor accuracy.
Figure 6 details the Sensitivity Check (Box 1). Box 2 provides test start instructions. Box 3 shows the initial 0.00 lbs sensor reading, within the acceptable range. Box 4 indicates the need for 66 lbs weight on the seat. Box 5 shows weights totaling 65 lbs being applied. Box 6 displays the sensor reading at 66.00 lbs, aligning with the applied weight and falling within the 59-73 lbs range. This SRS repair, demonstrating the power of a bidirectional function scan tool, would have been impossible without the proper equipment, including the scan tool, OEM software, and a weight set for calibration.
When Bidirectional Control Won’t Work as Expected
These examples showcase just a fraction of the applications for bidirectional function scan tools. The scan tools used often provide helpful information on test preparation and actuation procedures. However, situations may arise where a bidirectional control doesn’t actuate as expected or stops prematurely. Figure 7 illustrates such a scenario using screen captures from EASE Diagnostics and Vetronix scan tools.
Alt text: Comparison of bidirectional control information on EASE Diagnostics and Vetronix scan tools for purge solenoid, highlighting differences in test description, timeout notes, and actual solenoid behavior during testing.
The EASE Chrysler Enhanced software displays information about bidirectional controls. The “Test Description” box indicates a purge solenoid cycle of approximately 1.5 seconds, while the “Notes” box mentions a seven-minute timeout.
The white box with a blue border shows Mastertech screens from a 1995 Dodge Stratus, highlighting “Time On” and “Time Off” in red. At 3:52:59 p.m., the purge solenoid was commanded on. However, it automatically turned off after approximately 30 seconds, at 3:53:32 p.m. This automatic shut-off is a safety feature to protect the solenoid. Depending on the component and test, the solenoid might reactivate after a certain period.
This example demonstrates that information provided to scan tool manufacturers isn’t always perfectly accurate. Does this inaccuracy hinder diagnostics significantly? Not necessarily. A basic understanding of the test’s intended function is usually sufficient. In this case, the test successfully opened and closed the purge solenoid, fulfilling its diagnostic purpose. While accurate information is ideal, discrepancies can occur. Scan tool design specifications are often finalized before production vehicles roll off the assembly line. Vehicle engineers may make subsequent changes not reflected in the initial scan tool specifications. Furthermore, PCM reprogramming after vehicles are in service can alter bidirectional control behavior in ways not documented in the scan tool information.
The potential of bidirectional function scan tools in diagnostics is vast, and much more could be explored. To illustrate this depth, consider the GM Tech 2. GM provides “Tech 2 Pathing Tables,” a set of documents detailing the tool’s capabilities. These documents, categorized by Body, Powertrain, and Chassis, are 14 pages long and list over 1300 tests alphabetically – an astounding number! Tech 2 owners should acquire these documents from ACDelco (acdelcotds.com/store), Part No. ROM00190, for a comprehensive understanding of their scan tool’s bidirectional capabilities. GM also offers a handy pocket reference card, Part No. ROM00164.
For example, if a GM vehicle’s electric mirrors malfunction, and you want to test the Driver’s Electric Mirror using the Tech 2, the Body Pathing Table will guide you. Looking up “Driver’s Electric Mirror” reveals its location: Body-Memory Mirror Module-Special Functions-Output Controls. From there, you can command mirror movements in all directions using your bidirectional function scan tool.
Beyond mirror control, the Pathing Tables reveal a wide array of function tests, including Incandescent Dimming, Microphone Test, Military or Standard Time, Phone Call Test/OnStar, and Theater Dimming. This is just one manufacturer and one factory scan tool. Multiply this by numerous vehicle manufacturers, and the immense diagnostic power of bidirectional function scan tools becomes clear.
Can you afford to limit your service to older vehicles and basic engine control systems? Perhaps for now, but for how much longer? Investing in advanced bidirectional function scan tools is becoming increasingly essential. The long-term benefits in diagnostic efficiency and capability will far outweigh the initial cost.
