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DTC P0401: EGR Insufficient Flow

NOTE: Before you troubleshoot, record all freeze data and any on-board snapshot, and review GENERAL TROUBLESHOOTING INFORMATION .
  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 (A/T in P or N, M/T in neutral) 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)
    • A/T in D, M/T in 4th
    • 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 HDS screen indicate FAILED? 

    YES:  Clean the intake manifold EGR port and the EGR pipe with throttle plate cleaner (see EGR VALVE REPLACEMENT , and EGR PIPE REMOVAL AND INSTALLATION  ). Also, clean the passage inside the EGR valve with throttle plate cleaner, then go to step  9.

    NO:  If the HDS indicates PASSED, intermittent failure, the system is OK at this time. Check for poor connections or loose terminals at the EGR valve and the ECM/PCM. If the screen indicates EXECUTING, keep driving until a result comes on. If the screen indicates OUT OF CONDITION or NOT COMPLETED, go to step  5 and recheck.

  7. Turn the ignition switch to LOCK (0).
  8. Replace the EGR valve (see EGR VALVE REPLACEMENT  ).
  9. Turn the ignition switch to ON (II).
  10. Reset the ECM/PCM with the HDS.
  11. Do ECM/PCM IDLE LEARN PROCEDURE .
  12. Test-drive under these conditions:
    • Engine coolant temperature (ECT SENSOR 1) above 158°F (70°C)
    • A/Tin D, M/T in 4th
    • 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 ECM/PCM. If the connections and 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 HDS 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 ECM/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 or NOT COMPLETED, go to step  12.

  15. Update the ECM/PCM if it does not have the latest software (see ECM/PCM UPDATE ), or substitute a known-good ECM/PCM (see SUBSTITUTING THE ECM/PCM ).
  16. Test-drive under these conditions:
    • Engine coolant temperature (ECT SENSOR 1) above 158°F (70°C)
    • A/T in D, M/T in 4th
    • 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 ECM/PCM. If the ECM/PCM was updated, substitute a known-good ECM/PCM (see SUBSTITUTING THE ECM/PCM ), then go to step  16. If the ECM/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 HDS screen indicate PASSED? 

    YES:  If the ECM/PCM was updated, troubleshooting is complete. If the ECM/PCM was substituted, replace the original ECM/PCM (see ECM/PCM REPLACEMENT ). 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 ECM/PCM. if the ECM/PCM was updated, substitute a known-good ECM/PCM (see SUBSTITUTING THE ECM/PCM ), then go to step  16. If the ECM/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 or NOT COMPLETED, go to step  16.

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