DTC Troubleshooting
DTC P1078: IMT Valve Stuck in Low RPM PositionNOTE: Before you troubleshoot, record all freeze data and any on-board snapshot, and review the general troubleshooting information.
1. Turn the ignition switch ON (II).
2. Clear the DTC with the HDS.
3. Start the engine and hold the engine speed above 4,200 rpm.
4. Check the IMT VALVE CMD in the DATA LIST with the HDS.
Is OPEN indicated?
YES - Go to step 5.
NO - Go to step 32.
5. Check the IMT VALVE SW in the DATA LIST with the HDS.
Is CLOSE 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 OFF.
7. Disconnect the IMT actuator 5P connector.
8. Turn the ignition switch ON (II).
9. Measure 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 (C12) and the IMT actuator, then go to step 25.
10. Measure 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 15.
11. Turn the ignition switch OFF.
12. Jump the SCS line with the HDS.
13. Disconnect PCM connector C (44P).
14. Check for continuity between IMT actuator 5P connector terminal No. 2 and PCM connector terminal C39.
Is there continuity?
YES - Go to step 19.
NO - Repair open in the wire between the PCM (C39) and the IMT actuator, then go to step 25.
15. Turn the ignition switch OFF.
16. Jump the SCS line with the HDS.
17. Disconnect PCM connector B (44P).
18. Check for continuity between IMT actuator 5P connector terminal No. 3 and PCM connector terminal B31.
Is there continuity?
YES - Go to step 33.
NO - Repair open in the wire between the PCM (B31) and the IMT actuator, then go to step 25.
19. Check for continuity between PCM connector terminal C43 and body ground.
Is there continuity?
YES - Repair short in the wire between the PCM (C43) and the IMT actuator, then go to step 25.
NO - Go to step 20.
20. Check for continuity between IMT actuator 5P connector terminal No. 5 and PCM connector terminal C43.
Is there continuity?
YES - Go to step 21.
NO - Repair open in the wire between the PCM (C43) and the IMT actuator, then go to step 25.
21. Check for continuity between PCM connector terminal C44 and body ground.
Is there continuity?
YES - Repair short in the wire between the PCM (C44) and the IMT actuator, then go to step 25.
NO - Go to step 22.
22. Check for continuity between IMT actuator 5P connector terminal No. 4 and PCM connector terminal C44.
Is there continuity?
YES - Go to step 23.
NO - Repair open in the wire between the PCM (C44) and the IMT actuator, go to step 25.
23. Remove the IMT actuator.
24. Move the IMT valve by hand.
Does it move smoothly?
YES - Substitute a known-good IMT actuator, then go to step 25 and recheck. If DTC P1078 is not indicated, replace the IMT actuator, then go to step 25. If DTC P1078 is indicated, go to step 34.
NO - Remove the engine cover, and repair the stuck valve. If necessary, replace the intake manifold, then go to step 25.
25. Reconnect all connectors.
26. Turn the ignition switch ON (II).
27. Reset the PCM with the HDS.
28. Do the PCM idle learn procedure.
29. Start the engine. Hold the engine speed at 4,200 rpm for 10 seconds, then let it idle.
30. 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, 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 indicate PASSED?
YES - Troubleshooting is complete. If any other Temporary DTCs or DTCs were indicated in step 30, go to the indicated DTCs 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 29.
32. Turn the ignition switch OFF.
33. Reconnect all connectors.
34. Update the PCM if it does not have the latest software, or substitute a known-good PCM.
35. Start the engine. Hold the engine speed at 4,200 rpm for 10 seconds, then let it idle.
36. 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, then go to step 35. If the PCM was substituted, go to step 1.
NO - Go to step 37.
37. 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. If any other Temporary DTCs or DTCs were indicated in step 36, go to the indicated DTCs 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, then go to step 35. If the PCM was substituted, go to step 1. If the screen indicates NOT COMPLETED, go to step 35.