DTC Troubleshooting

DTC Troubleshooting: P0401

DTC P0401:

EGR Insufficient Flow

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. Hold the engine speed at 3,000 rpm without load (in P or N) until the radiator fan comes on, then let it idle.

4. Do the EGR TEST in the INSPECTION MENU with the HDS.

Is the result OK?

YES -

Go to step 5.

NO -

Go to step 7.

5. Test-drive under these conditions:

- Engine coolant temperature (ECT SENSOR 1) above 158 °F (70 °C)
- Transmission in D
- Drive at a steady speed between 55-75 mph (88-120 km/h) for at least 10 seconds
- During the drive, decelerate (with the throttle fully closed) for 5 seconds

6. Monitor the OBD STATUS for DTC P0401 in the DTCs MENU with the HDS.

Does the screen indicate FAILED?

YES -

Clean the intake manifold EGR port and the EGR pipe Service and Repair with throttle plate cleaner. Also, clean the passage inside the EGR valve with throttle plate cleaner, then go to step 9.

NO -

If the screen indicates PASSED, intermittent failure, the system is OK at this time. Check for poor connections or loose terminals at the EGR valve and the PCM. If the screen indicates EXECUTING, keep driving until a result comes on. If the screen indicates OUT OF CONDITION, go to step 5 and recheck.

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

8. Replace the EGR valve Service and Repair.

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

10. Reset the PCM with the HDS.

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

12. Test-drive under these conditions:

- Engine coolant temperature (ECT SENSOR 1) above 158 °F (70 °C)
- Transmission in D
- Drive at a steady speed between 55-75 mph (88-120 km/h) for at least 10 seconds
- During the drive, decelerate (with the throttle fully closed) for 5 seconds

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

Is DTC P0401 indicated?

YES -

Check for poor connections or loose terminals at the EGR valve and the PCM. If the connections and the terminals are OK, go to step 15.

NO -

Go to step 14.

14. Monitor the OBD STATUS for DTC P0401 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 13, go to the indicated DTC's troubleshooting.�

NO -

If the screen indicates FAILED, check for poor connections or loose terminals at the EGR valve and the PCM, then go to step 1. If the screen indicates EXECUTING, keep driving until a result comes on. If the screen indicates OUT OF CONDITION, go to step 12.

15. Update the PCM if it does not have the latest software PCM Update, or substitute a known-good PCM.

16. Test-drive under these conditions:

- Engine coolant temperature (ECT SENSOR 1) above 158 °F (70 °C)
- Transmission in D
- Drive at a steady speed between 55-75 mph (88-120 km/h) for at least 10 seconds
- During the drive, decelerate (with the throttle fully closed) for 5 seconds

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

Is DTC P0401 indicated?

YES -

Check for poor connections or loose terminals at the EGR valve and the PCM. If the PCM was updated, substitute a known-good PCM, then go to step 16. If the PCM was substituted, go to step 1.

NO -

Go to step 18.

18. Monitor the OBD STATUS for DTC P0401 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 17, go to the indicated DTC's troubleshooting.�

NO -

If the screen indicates FAILED, check for poor connections or loose terminals at the EGR valve and the PCM. If the PCM was updated, substitute a known-good PCM, then go to step 16. If the PCM was substituted, go to step 1. If the screen indicates EXECUTING, keep driving until a result comes on. If the screen indicates OUT OF CONDITION, go to step 16.