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), or press the engine start/stop button to select the ON mode.

2. Clear the DTC with the HDS.

3. Do the IMT TEST in the INSPECTION MENU with the HDS.

Is the result OK?
YES - Intermittent failure, the system is OK at this time. Check for poor connections or loose terminals at the IMT actuator and the PCM.

NO - Go to step 4.


4. Turn the ignition switch to LOCK (0), or press the engine start/stop button to select the OFF mode.

5. Disconnect the IMT actuator 5P connector.

6. Turn the ignition switch to ON (II), or press the engine start/stop button to select the ON mode.

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

Is CLOSE indicated?
YES - Go to step 12.

NO - Go to step 8.


8. Turn the ignition switch to LOCK (0), or press the engine start/stop button to select the OFF mode.

9. Jump the SCS line with the HDS.

10. Disconnect PCM connector B (49P).

11. 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 24.

NO - Go to step 31.






12. Turn the ignition switch to LOCK (0), or press the engine start/stop button to select the OFF mode.

13. Jump the SCS line with the HDS.

14. Disconnect PCM connector C (49P).

15. 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 24.

NO - Go to step 16.






16. 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 24.

NO - Go to step 17.






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

Is there continuity?
YES - Go to step 18.

NO - Repair open in the wire between the PCM (C48) and the IMT actuator, then go to step 24.






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

Is there continuity?
YES - Go to step 19.

NO - Repair open in the wire between the PCM (C49) and the IMT actuator, then go to step 24.






19. Remove the IMT actuator. Service and Repair

20. Move the IMT valve by hand.

Does it move smoothly?
YES - Go to step 21.

NO - Remove the intake manifold upper cover, Intake Manifold Removal and Installation and repair the stuck valve. If needed, replace the intake manifold, Intake Manifold Removal and Installation then go to step 24.


21. Substitute a known-good IMT actuator. Service and Repair

22. Turn the ignition switch to ON (II), or press the engine start/stop button to select the ON mode.

23. Do the IMT TEST in the INSPECTION MENU with the HDS.

Is the result OK?
YES - Replace the original IMT actuator, Service and Repair then go to step 24.

NO - Go to step 32.


24. Reconnect all connectors.

25. Turn the ignition switch to ON (II), or press the engine start/stop button to select the ON mode.

26. Reset the PCM with the HDS.

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

28. Start the engine, and let it idle without load (in P or N) until the radiator fan comes on.

29. Hold the engine speed at 4,000 rpm for 3 seconds or more, then let it idle.

30. 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 31.


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

Does the screen indicates PASSED?
YES - Troubleshooting is complete. If any other Pending or Confirmed DTCs were indicated in step 30, 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, go to step 28.


32. Reconnect all connectors.

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

34. Start the engine, and let it idle without load (in P or N) until the radiator fan comes on.

35. Hold the engine speed at 4,000 rpm for 3 seconds or more, then let it idle.

36. 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, Initial Inspection and Diagnostic Overview then go to step 34. If the PCM was substituted, go to step 1.

NO - Go to step 37.


37. Monitor the OBD STATUS for DTC P1078 in the DTC's 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.. PCM Replacement If any other Pending or Confirmed DTCs were indicated in step 36, go to the indicated DTC's troubleshooting.

NO - If the screen indicated 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 go to step 34. If the PCM was substituted, go to step 1. If the screen indicates NOT COMPLETED, go to step 34.