DTC Troubleshooting

DTC Troubleshooting: P0641

DTC P0641: Sensor Reference Voltage A Malfunction

NOTE: Before you troubleshoot, record all freeze data and any on-board snapshot, and review the general troubleshooting information. Initial Inspection and Diagnostic Overview

1. Turn the ignition switch to ON (II).

2. Clear the DTC with the HDS.

3. Check for Temporary DTCs or DTCs with the HDS.

Is DTC P0641 indicated?
YES - Go to step 4.

NO - Intermittent failure, the system is OK at this time. Check for poor connections or loose terminals at the ECM/PCM and these connectors:

- Throttle body

- EGR valve

- Input shaft (mainshaft) speed sensor

- APP sensor



4. Turn the ignition switch to LOCK (0).

5. Disconnect these connectors:
- Throttle body

- EGR valve

- Input shaft (mainshaft) speed sensor

- APP sensor

6. Turn the ignition switch ON (II).

7. Clear the DTC with the HDS.

8. Check for Temporary DTCs or DTCs with the HDS.

Is DTC P0641 indicated?
YES - Go to step 10.

NO - Go to step 9.


9. Check for Temporary DTCs or DTCs with the HDS while connecting each these connectors:
- Throttle body

- EGR valve

- Input shaft (mainshaft) speed sensor

- APP sensor

Is DTC P0641 indicated?
YES - Replace the parts connected when the DTC is indicated, then go to step 14.

NO - Check for poor connections or loose terminals at the ECM/PCM and these connectors:

- Throttle body

- EGR valve

- Input shaft (mainshaft) speed sensor

- APP sensor

If the connections and terminals are OK, go to step 1 and recheck.


10. Turn the ignition switch to LOCK (0).

11. Jump the SCS line with the HDS.

12. Disconnect ECM/PCM connectors A (49P), B (49P), and C (49P).

13. Check for continuity between body ground and ECM/PCM connector terminals A24, B18, and C12 individually.

Is there continuity?
YES - Repair short in the wire between the ECM/PCM (A24, B18, or C12) and each sensor, then go to step 14.

NO - Go to step 20.






14. Turn the ignition switch to LOCK (0).

15. Reconnect all connectors.

16. Turn the ignition switch to ON (II).

17. Reset the ECM/PCM with the HDS.

18. Do the ECM/PCM idle learn procedure. ECM/PCM Idle Learn Procedure

19. Check for Temporary DTCs or DTCs with the HDS.

Is DTC P0641 indicated?
YES - Check for poor connections or loose terminals at the ECM/PCM and these connectors:

- Throttle body

- EGR valve

- Input shaft (mainshaft) speed sensor

- APP sensor

If the connections and the terminals are OK, go to step 1 and recheck.

NO - Troubleshooting is complete. If any other Temporary DTCs or DTCs are indicated, go to the indicated DTC's troubleshooting.


20. Reconnect all connectors.

21. Update the ECM/PCM if it does not have the latest software, ECM/PCM Update or substitute a known-good ECM/PCM. Initial Inspection and Diagnostic Overview

22. Check for Temporary DTCs or DTCs with the HDS.

Is DTC P0641 indicated?
YES - If the ECM/PCM was updated, substitute a known-good ECM/PCM, Initial Inspection and Diagnostic Overview then recheck. If the ECM/PCM was substituted, check for poor connections or loose terminals at the ECM/PCM and these connectors:

- Throttle body

- EGR valve

- Input shaft (mainshaft) speed sensor

- APP sensor

If the connections and the terminals are OK, go to step 1.

NO - If the ECM/PCM was updated, troubleshooting is complete. If the ECM/PCM was substituted, replace the original ECM/PCM. Service and Repair If any other Temporary DTCs or DTCs are indicated, go to the indicated DTC's troubleshooting.