Experiencing a Diagnostic Trouble Code (DTC) P0122 on your 2003 Silverado 6.0 and seeing a disheartening 0 voltage reading for the Throttle Position Sensor (TPS) on your scan tool? This situation can be frustrating, potentially leading to poor engine performance and drivability issues. As an automotive expert at vcdstool.com, I’m here to guide you through understanding and resolving this problem effectively. This comprehensive guide will delve into the intricacies of DTC P0122, focusing on a 0 voltage scenario, and provide a step-by-step diagnostic approach to get your Silverado back on the road.
Understanding DTC P0122 and the TPS
DTC P0122, as defined by GM’s SI2000 system, indicates a “Throttle Position (TP) Sensor Circuit Low Voltage”. The TPS is essentially a potentiometer mounted on the throttle body. Its crucial role is to monitor the throttle blade angle and relay this information as a voltage signal to the Powertrain Control Module (PCM). This signal is a primary input for the PCM, influencing vital engine functions like fuel delivery, ignition timing, and transmission control.
Typically, a healthy TPS on a 2003 Silverado 6.0 should register around 0.6 volts at idle and increase to over 4.0 volts when the throttle is wide open (WOT). When the PCM detects a TPS signal voltage that falls below the expected operating range, specifically less than 0.2 volts for a sustained period, it triggers the P0122 code. The concerning scenario we’re addressing here is when your scan tool reads 0 voltage, indicating a severe low voltage condition.
Conditions for Setting and Clearing DTC P0122
For DTC P0122 to set, certain conditions must be met:
- The ignition switch must be in the ON position, or the engine must be running.
- The TPS signal voltage must be less than 0.2 volts for 10 seconds continuously.
When DTC P0122 is active, you might experience several consequences:
- Malfunction Indicator Lamp (MIL): The check engine light will illuminate, usually after the second consecutive ignition cycle where the fault is detected.
- PCM Default Value: The PCM will use a default value for the TPS, which can lead to compromised engine performance.
- Transmission Issues: Torque Converter Clutch (TCC) may not apply, high transmission line pressure, fixed and harsh shift points, and potentially no fourth gear in “hot mode”.
Fortunately, clearing the DTC is possible if the issue is resolved:
- The MIL will turn off after three consecutive ignition cycles where the diagnostic runs and passes.
- A history DTC will clear after 40 consecutive warm-up cycles without any reported failures.
- You can also manually clear the DTC and MIL using a scan tool.
Diagnosing 0 Voltage on the TPS for a 2003 Silverado 6.0
When your scan tool shows 0 voltage for the TPS on your 2003 Silverado 6.0, it’s a strong indicator of a problem within the TPS circuit. Here’s a systematic diagnostic approach based on the original GM SI2000 diagnostic table, expanded for clarity and practical application:
Step 1: Initial OBD System Check & DTC Verification
- Begin by performing a complete Powertrain On-Board Diagnostic (OBD) system check using your scan tool.
- Idle the engine and monitor DTC information.
- If DTC P1639 (5 Volt Reference 2 Circuit) is present alongside P0122, it suggests a potential short to ground or voltage in the 5-volt reference circuit. This is crucial information as the TPS relies on this reference voltage. Address P1639 first if present.
- Specifically check if DTC P0122 is failing in the current ignition cycle.
Step 2: Confirm Low Voltage with Throttle Closed
- Turn the ignition ON, engine OFF.
- With the throttle fully closed, observe the TPS voltage reading on your scan tool.
- Expected Outcome: The voltage should ideally be around 0.6V. If it’s reading 0V or below 0.2V, proceed to the next steps. If it’s above 0.2V but still causing issues, consult the Diagnostic Aids section later.
Step 3: Review Freeze Frame Data and Replicate Conditions
- If the voltage was not below 0.2V in Step 2, review Freeze Frame and/or Failure Records data for DTC P0122. This data captures the operating conditions when the DTC was set.
- Record parameters like RPM, load, vehicle speed, and temperature.
- Turn the ignition OFF for 15 seconds, then restart the engine.
- Attempt to operate the vehicle under the conditions recorded in the Freeze Frame data to try and replicate the fault and confirm if the DTC resets.
- Monitor if the scan tool indicates the diagnostic failed in this ignition cycle. If it does, proceed to Step 5. If not, the issue might be intermittent, and refer to “Diagnostic Aids” section later.
Step 4: Isolate Potential Short with Accelerator and Servo Control Module (ASCM)
- Important: Before proceeding, understand that this step involves disconnecting the ASCM. After this diagnosis, remember to reconnect it and clear any ASCM related DTCs that might set during disconnection.
- Turn OFF the ignition.
- Disconnect the Accelerator and Servo Control Module (ASCM). Refer to your Silverado service manual for the location and disconnection procedure.
- Turn ON the ignition, engine OFF.
- Check the TPS voltage on the scan tool again.
- Interpretation:
- If the TPS voltage remains below 0.2V: The issue is likely NOT within the ASCM. Proceed to Step 6.
- If the TPS voltage is now above 0.2V: The ASCM or its related wiring might be the cause of the low voltage condition. Investigate the ASCM and its wiring. Perform a “Diagnostic System Check in Antilock Brake System” as indicated in the original document, although this might be a misdirection in the original text and perhaps refers to a general system check. Focus on inspecting the ASCM wiring harness for shorts or damage.
Step 5: Jumper Test at TPS Connector (5V Reference to Signal)
- Turn OFF the ignition.
- Disconnect the electrical connector at the TPS.
- Locate the 5-volt reference circuit and the TPS signal circuit in the connector. Refer to a wiring diagram for your 2003 Silverado 6.0.
- Using a jumper wire, carefully connect the 5-volt reference circuit terminal to the TPS signal circuit terminal on the harness side connector (not the sensor side).
- Turn ON the ignition, engine OFF.
- Observe the TPS voltage reading on the scan tool.
- Expected Outcome: The voltage should jump up to around 4.7V or higher.
- Interpretation:
- If voltage is above 4.7V: This indicates the wiring between the PCM and the TPS, including the 5V reference and signal circuits, is likely intact. The problem could be the TPS sensor itself (proceed to Step 12) or potentially the sensor ground circuit (though less likely with a 0V reading).
- If voltage is still low (not above 4.7V): There’s a problem in the wiring between the TPS connector and the PCM, or potentially with the PCM itself. Proceed to Step 7.
Step 6: Test Lamp on TPS Signal Circuit
- Keep the TPS connector disconnected.
- Connect a test lamp (J 34142-B or equivalent) between battery positive (B+) and the TPS signal circuit terminal on the harness side of the TPS connector.
- Turn ON the ignition, engine OFF.
- Observe the TPS voltage reading on the scan tool.
- Expected Outcome: The voltage should now be above 4.7V.
- Interpretation:
- If voltage is above 4.7V: This confirms the issue is likely in the sensor ground circuit or the TPS sensor itself (less likely sensor ground with 0V reading). Proceed to Step 8 to investigate the 5V reference circuit wiring and PCM.
- If voltage is still low (not above 4.7V): The problem lies in the TPS signal circuit wiring or potentially the PCM. Proceed to Step 10 to investigate the signal circuit wiring and PCM.
Step 7: 5V Reference Circuit Testing (Open or Short to Ground)
- Turn OFF the ignition.
- Disconnect PCM connector C2 (refer to your service manual for location).
- Test the 5-volt reference circuit wire (between the PCM connector C2 and the TPS connector) for:
- Open Circuit: Use a multimeter in continuity mode to check for breaks in the wire.
- Short to Ground: Use a multimeter to measure resistance between the 5V reference wire and ground. A low resistance (close to 0 ohms) indicates a short to ground.
- Repair any identified wiring issues (opens or shorts) as needed.
Step 8: 5V Reference Circuit Poor Connection at PCM
- If no wiring issues were found in Step 7, suspect a poor connection in the 5-volt reference circuit at the PCM connector C2.
- Inspect the PCM connector terminals for corrosion, damage, or looseness.
- Clean and repair any poor connections as necessary.
Step 9: TPS Signal Circuit Testing (Open, Short to Ground, or Short to Sensor Ground)
- Turn OFF the ignition and disconnect PCM connector C2 if not already disconnected.
- Test the TPS signal circuit wire (between the PCM connector C2 and the TPS connector) for:
- Open Circuit: Check for continuity.
- Short to Ground: Check resistance to ground.
- Short to Sensor Ground Circuit: Check for continuity or resistance between the TPS signal wire and the sensor ground wire.
- Repair any wiring issues found.
Step 10: TPS Signal Circuit Poor Connection at PCM
- If no wiring issues were found in Step 9, check for poor connection in the TPS signal circuit at the PCM connector C2.
- Inspect, clean, and repair any poor connections.
Step 11: TPS Sensor Replacement
- If all wiring and PCM connector issues have been ruled out, and the tests point towards a sensor problem (especially if Step 5 indicated wiring was likely okay), replace the TPS sensor. Refer to your service manual for the replacement procedure.
Step 12: PCM Replacement (Last Resort)
- PCM replacement is generally considered a last resort after all other possibilities have been exhausted, especially wiring and sensor issues. If all tests point to a PCM fault and replacing the TPS didn’t resolve the 0 voltage issue, PCM replacement might be necessary.
- Important: PCM replacement often requires programming to match your vehicle’s VIN and options. Consult your service manual and consider professional programming services if needed.
Step 13: Verify Repair and Clear DTCs
- After completing any repairs (wiring, sensor, or PCM replacement), reconnect all components, including the ASCM if it was disconnected.
- Use your scan tool to clear all DTCs.
- Start the engine and let it reach normal operating temperature.
- Monitor the TPS voltage reading on the scan tool to ensure it is now within the normal range (around 0.6V at idle, increasing with throttle).
- Use the scan tool to run the DTC P0122 diagnostic test again to confirm it now passes.
- Operate the vehicle under conditions that previously triggered the DTC to ensure the issue is resolved.
Step 14: Final DTC Check
- After testing and driving, perform a final scan for DTCs.
- If DTC P0122 is gone and no other related DTCs are present, the system is likely OK.
- If any other DTCs are present, diagnose them using the appropriate diagnostic procedures.
Diagnostic Aids and Intermittent Issues
- Intermittent Faults: A 0 voltage reading can sometimes be caused by intermittent issues like:
- Mis-routed wiring harness.
- Rubbed-through wire insulation causing shorts.
- Broken wires inside the insulation.
- Loose or corroded connectors.
- Freeze Frame Data: Utilize Freeze Frame and Failure Records data to understand the conditions under which the DTC originally set. This can be invaluable for diagnosing intermittent problems by helping you recreate the fault conditions.
- Connector Inspection: Pay close attention to PCM and TPS connector surfaces. Ensure they are clean and free of debris. Inspect PCM connector gaskets for correct installation to prevent contamination.
- Special Tools: Using a Connector Test Adapter Kit (like J 35616-A) when probing PCM or component harness connectors is crucial to prevent damage to the terminals.
- 5V Reference Circuit Sharing: Be aware that the 5-volt reference circuit is often shared by multiple sensors (e.g., Fuel Tank Pressure Sensor). If all TPS circuits seem okay, investigate other sensors sharing the 5V reference if you suspect a broader 5V reference issue.
Conclusion
Diagnosing a 2003 Silverado 6.0 TPS showing 0 voltage on a scan tool requires a systematic approach. By meticulously following these diagnostic steps, focusing on wiring integrity, sensor functionality, and PCM health, you can effectively pinpoint the root cause of the P0122 code. Remember to prioritize safety, use proper tools, and consult your vehicle’s service manual for specific procedures and wiring diagrams. With patience and careful troubleshooting, you can restore your Silverado’s performance and eliminate that frustrating 0 voltage reading.
