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DTC P0401

DTC P0401  EGR flow insufficient detected 
DETECTION CONDITION 
  • The PCM monitors difference in intake manifold pressures when EGR is operated and when it is stopped. If the difference is too small, the PCM determines that EGR flow insufficient.

Diagnostic support note 
  • This is an intermittent monitor (EGR system).
  • The MIL illuminates if the PCM detects above malfunction condition in two consecutive drive cycles or in one drive cycle while the DTC for the same malfunction has been stored in the PCM.
  • PENDING CODE is available if the PCM detects the above malfunction condition during the first drive cycle.
  • FREEZE FRAME DATA (Mode 2/Mode 12) is available.
  • The DTC is stored m me PCM memory.
POSSIBLE CAUSE 
  • MAP sensor malfunction
  • EGR valve malfunction
  • EGR valve passage malfunction
    • Gasket of EGR valve malfunction
    • Clogged EGR valve passage
  • PCM malfunction
DIAGNOSTIC PROCEDURE

STEP INSPECTION ACTION
1 VERIFY FREEZE FRAME DATA (MODE 12) AND DIAGNOSTIC MONITORING TEST RESULTS HAVE BEEN RECORDED 
  • Have the FREEZE FRAME DATA (Mode 12) and DIAGNOSTIC MONITORING TEST RESULTS (EGR system related) been recorded?
 Yes Go to the next step.
No Record the FREEZE FRAME DATA (Mode 12) and DIAGNOSTIC MONITORING TEST RESULTS on the repair order, then go to the next step.
2 VERIFY RELATED SERVICE BULLETINS AVAILABILITY 
  • Verify related Service Bulletins availability.
  • Is any related Service Bulletins available?
 Yes Perform the repair or diagnosis according to the available Service Bulletins.
  • If the vehicle is not repaired, go to the next step.
No Go to the next step.
3 VERIFY RELATED PENDING CODE AND STORED DTC 
  • Turn the ignition switch off then to the ON position (Engine off).
  • Verify the related PENDING CODE and stored DTC.
  • Are any DTCs present?
 Yes Go to the applicable DTC inspection.
(See DTC TABLE ).
No Go to the next step.
4 INSPECT MAP SENSOR 
 Yes Replace the MAP sensor, then go to Step 7.
(See MANIFOLD ABSOLUTE PRESSURE (MAP) SENSOR REMOVAL/INSTALLATION ).
No Go to the next step.
5 INSPECT EGR VALVE OPERATION 
 Yes Go to the next step.
No Repair or replace the malfunctioning part according to the inspection results, then go to Step 7.
6 INSPECT EGR VALVE PASSAGE 
 Yes Go to the next step.
No Install the gasket correctly, then go to the next step.
7 VERIFY TROUBLESHOOTING OF DTC P0401 COMPLETED 
  • Clear the DTC from the PCM memory using the M-MDS.
  • Perform the Drive Mode 03 (PCM Adaptive Memory Production, EGR System, A/F Sensor Heater, HO2S Heater, A/F Sensor, HO2S, and TWC Repair Verification Drive Mode).

    (See OBD-II DRIVE MODE ).

  • Stop the vehicle and access the ON BOARD READINESS TEST to inspect the Drive Mode completion status.
  • Verify that the ON BOARD READINESS TEST status changing to YES.
  • Perform the Diagnostic Monitoring Test Results Access Procedure.

    (See ON-BOARD DIAGNOSTIC TEST ).

  • Verify the #31:83 (EGR pressure variation) value.

    (See DIAGNOSTIC MONITORING TEST RESULTS ).

  • Is the value out of the specification?
 Yes Replace the PCM, then go to the next step.
(See PCM REMOVAL/INSTALLATION ).
No Retry this step.
8 VERIFY AFTER REPAIR PROCEDURE 
 Yes Go to the applicable DTC inspection.
(See DTC TABLE ).
No DTC troubleshooting completed.
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