DTC Troubleshooting

DTC Troubleshooting: P1078

DTC P1078: IMT Valve Stuck in Low RPM Position

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. Start the engine, and let it idle.

4. Check the IMT VALVE CMD in the DATA LIST with the HDS.

Is CLOSE indicated?
YES - Go to step 5.

NO - Go to step 29.


5. Check the IMT VALVE SW in the DATA LIST with the HDS.

Is OPEN indicated?
YES - Go to step 6.

NO - Intermittent failure, the system is OK at this time. Check for poor connections or loose terminals at the IMT actuator and the PCM.


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

7. Disconnect the IMT actuator 5P connector.

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

9. Check the IMT VALVE SW in the DATA LIST with the HDS.

Is CLOSE indicated?
YES - Go to step 14.

NO - Go to step 10.


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

11. Jump the SCS line with the HDS.

12. Disconnect PCM connector B (49P).

13. Check for continuity between PCM connector terminal B19 and body ground.

Is there continuity?
YES - Repair short in the wire between the PCM (B19) and the IMT actuator, then go to step 23.

NO - Go to step 30.






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

15. Jump the SCS line with the HDS.

16. Disconnect PCM connector C (49P).

17. Check for continuity between PCM connector terminal C48 and body ground.

Is there continuity?
YES - Repair short in the wire between the PCM (C48) and the IMT actuator, then go to step 23.

NO - Go to step 18.






18. Check for continuity between PCM connector terminal C48 and IMT actuator 5P connector terminal No. 5.

Is there continuity?
YES - Go to step 19.

NO - Repair open in the wire between the PCM (C48) and the IMT actuator, then go to step 23.






19. Check for continuity between PCM connector terminal C49 and body ground.

Is there continuity?
YES - Repair short in the wire between the PCM (C49) and the IMT actuator, then go to step 23.

NO - Go to step 20.






20. Check for continuity between PCM connector terminal C49 and IMT actuator 5P connector terminal No. 4.

Is there continuity?
YES - Go to step 21.

NO - Repair open in the wire between the PCM (C49) and the IMT actuator, then go to step 23.






21. Remove the IMT actuator. Service and Repair

22. Move the IMT valve by hand.

Does it move smoothly?
YES - Substitute a known-good IMT actuator, Service and Repair then go to step 23 and recheck. If DTC P1077 is not indicated, replace the IMT actuator, Service and Repair then go to step 23. If DTC P1077 is indicated, go to step 31.

NO - Remove the engine cover, Intake Manifold Removal and Installation and repair the stuck valve. If necessary, replace the intake manifold, Intake Manifold Removal and Installation then go to step 23.


23. Reconnect all connectors.

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

25. Reset the PCM with the HDS.

26. Do the PCM idle learn procedure. PCM Idle Learn Procedure

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

Is DTC P1077 indicated?
YES - Check for poor connections or loose terminals at the IMT actuator and the PCM. If the PCM was updated, substitute a known-good PCM, Initial Inspection and Diagnostic Overview then recheck. If the PCM was substituted, go to step 1.

NO - Go to step 28.


28. Monitor the OBD STATUS for DTC P1078 in the DTCs MENU with the HDS.

Does the screen indicate PASSED?
YES - If the PCM was updated, troubleshooting is complete. If the PCM was substituted, replace the original PCM. Service and Repair If any other Temporary DTCs or DTCs were indicated in step 27, go to the indicated DTC's troubleshooting.

NO - If the screen indicates FAILED, check for poor connections or loose terminals at the IMT actuator and the PCM. If the PCM was updated, substitute a known-good PCM, Initial Inspection and Diagnostic Overview then recheck. If the PCM was substituted, go to step 1. If the screen indicates NOT COMPLETED, keep idling until a result comes on.


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

30. Reconnect all connectors.

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

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

Is DTC P1078 indicated?
YES - Check for poor connections or loose terminals at the IMT actuator and the PCM. If the PCM was updated, substitute a known-good PCM, Initial Inspection and Diagnostic Overview then recheck. If the PCM was substituted, go to step 1.

NO - Go to step 33.


33. Monitor the OBD STATUS for DTC P1078 in the DTCs MENU with the HDS.

Does the screen indicate PASSED?
YES - If the PCM was updated, troubleshooting is complete. If the PCM was substituted, replace the original PCM. Service and Repair If any other Temporary DTCs or DTCs were indicated in step 32, go to the indicated DTC's troubleshooting.

NO - If the screen indicates FAILED, check for poor connections or loose terminals at the IMT actuator and the PCM. If the PCM was updated, substitute a known-good PCM, Initial Inspection and Diagnostic Overview then recheck. If the PCM was substituted, go to step 1. If the screen indicates NOT COMPLETED, keep idling until a result comes on.