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. Reading and Clearing Diagnostic Trouble Codes

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

2. Clear the DTC with the HDS.

3. Start the engine. Hold the engine speed above 4,000 rpm.

4. Make sure the IMT VALVE CMD is OPEN in the DATA LIST with the HDS.

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

Is CLOSED 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. Let the engine idle, then turn the ignition switch to LOCK (0).

7. Disconnect the IMT actuator 5P connector.

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

9. Measure the voltage between IMT actuator 5P connector terminal No. 1 and body ground.

Is there about 5 V?
YES - Go to step 10.

NO - Repair open in the wire between the PCM (C14) and the IMT actuator, then go to step 27.






10. Measure the voltage between IMT actuator 5P connector terminal No. 3 and body ground.

Is there about 5 V?
YES - Go to step 11.

NO - Go to step 16.






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

12. Jump the SCS line with the HDS.

13. Disconnect PCM connector C (22P).

14. Connect IMT actuator 5P connector terminal No. 2 to body ground with a jumper wire.






15. Check for continuity between PCM connector terminal C12 and body ground.

Is there continuity?
YES - Go to step 21.

NO - Repair open in the wire between the PCM (C12) and the IMT actuator, then go to step 29.






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

17. Jump the SCS line with the HDS.

18. Disconnect PCM connector B (24P).

19. Connect IMT actuator 5P connector terminal No. 3 to body ground with a jumper wire.






20. Check for continuity between PCM connector terminal B11 and body ground.

Is there continuity?
YES - Go to step 36.

NO - Repair open in the wire between the PCM (B11) and the IMT actuator, then go to step 27.






21. Check for continuity between PCM connector terminal B4 and body ground.

Is there continuity?
YES - Repair short in the wire between the PCM (B4) and the IMT actuator, then go to step 29.

NO - Go to step 22.






22. Connect IMT actuator 5P connector terminal No. 5 to body ground with a jumper wire.






23. Check for continuity between PCM connector terminal B4 and body ground.

Is there continuity?
YES - Go to step 24.

NO - Repair open in the wire between the PCM (B4) and the IMT actuator, then go to step 29.






24. Check for continuity between PCM connector terminal B3 and body ground.

Is there continuity?
YES - Repair short in the wire between the PCM (B3) and the IMT actuator, then go to step 29.

NO - Go to step 25.






25. Connect IMT actuator 5P connector terminal No. 4 to body ground with a jumper wire.






26. Check for continuity between PCM connector terminal B3 and body ground.

Is there continuity?
YES - Go to step 27.

NO - Repair open in the wire between the PCM (B3) and the IMT actuator, go to step 29.






27. Remove the IMT actuator. Service and Repair

28. Move the IMT valve by hand.

Does it move smoothly?
YES - Substitute a known-good IMT actuator, Service and Repair then go to step 29 and recheck. If DTC P1078 is not indicated, replace the IMT actuator, Service and Repair then go to step 29. If DTC P1078 is indicated, go to step 37.

NO - Remove the engine cover, Intake Manifold Removal/Installation and repair the stuck valve. If needed, replace the intake manifold, Intake Manifold Removal/Installation then go to step 29.


29. Reconnect all connectors.

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

31. Reset the PCM with the HDS.

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

33. Start the engine. Hold the engine speed at 4,000 rpm for 10 seconds, then let it idle.

34. Check for Pending or Confirmed DTCs with the HDS.

Is DTC P1078 indicated?
YES - Check for poor connections or loose terminals at the IMT actuator and the PCM, then go to step 1.

NO - Go to step 35.


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

Does the screen indicate PASSED?
YES - Troubleshooting is complete. If any other Pending or Confirmed DTCs were indicated in step 34, 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, then go to step 1. If the screen indicates NOT COMPLETED, keep idling until a result comes on.


36. Reconnect all connectors.

37. Update the PCM if it does not have the latest software, PCM Update or substitute a known-good PCM. Reading and Clearing Diagnostic Trouble Codes

38. Start the engine, and hold the engine speed at 4,000 rpm for 10 seconds, then let it idle.

39. Check for Pending or Confirmed 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, Reading and Clearing Diagnostic Trouble Codes then go to step 38. If the PCM was substituted, go to step 1.

NO - Go to step 40.


40. 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 Pending or Confirmed DTCs were indicated in step 39, 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, Reading and Clearing Diagnostic Trouble Codes then go to step 38. If the PCM was substituted, go to step 1. If the screen indicates NOT COMPLETED, go to step 38.