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2008 - MX-5 - Engine

DTC P0401 [LF]



DTC P0401

EGR flow insufficient detected

DETECTION CONDITION

  • PCM monitors difference in intake manifold pressures when EGR is operated and when it is stopped. If the difference is too small, 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 is available.

  • The DTC is stored in the PCM memory.

POSSIBLE CAUSE

  • EGR valve malfunction

  • MAP sensor malfunction

  • EGR gasket malfunction

  • PCM malfunction


Diagnostic procedure

STEP

INSPECTION

ACTION

1

VERIFY FREEZE FRAME DATA AND DIAGNOSTIC MONITORING TEST RESULTS HAVE BEEN RECORDED
  • Have FREEZE FRAME DATA and DIAGNOSTIC MONITORING TEST RESULTS (EGR system related) been recorded?

Yes

Go to the next step.

No

Record FREEZE FRAME DATA and DIAGNOSTIC MONITORING TEST RESULTS on the repair order, then go to the next step.

2

VERIFY RELATED REPAIR INFORMATION AVAILABILITY
  • Verify related Service Bulletins and/or on-line repair information availability.

  • Is any related repair information available?

Yes

Perform repair or diagnosis according to the available repair information.

  • If the vehicle is not repaired, go to the next step.

No

Go to the next step.

3

INSPECT FOR OTHER DTCS
  • Turn the ignition switch off then to the ON position (Engine off).

  • Have other DTCs been stored?

Yes

Repair circuit malfunction for applicable DTCs.

No

Go to the next step.

4

INSPECT VACUUM HOSE CONDITION
  • Inspect vacuum hoses for clogs, any damages, frozen, or vacuum leakage.

  • Is there any malfunction?

Yes

Replace vacuum hoses, then go to Step 8.

No

Go to the next step.

5

INSPECT EGR VALVE MALFUNCTION

Yes

Go to the next step.

No

Replace the EGR valve, then go to Step 8.

(See EGR VALVE REMOVAL/INSTALLATION [LF].)

6

INSPECT MAP SENSOR MALFUNCTION

Yes

Go to the next step.

No

Replace MAP sensor, then go to Step 8.

(See MANIFOLD ABSOLUTE PRESSURE (MAP) SENSOR REMOVAL/INSTALLATION [LF].)

7

INSPECT EGR VALVE PASSAGE
  • Turn the ignition switch off.

  • Remove the EGR valve.

  • Is gasket installation normal?

Yes

Go to the next step.

No

Install gasket correctly, then go to the next step.

8

MONITOR EGR SYSTEM BY DRIVE MODE
  • Clear DTC from PCM memory using M-MDS.

  • Run PCM Adaptive Memory Procedure Drive Mode.

    (See OBD-II DRIVE MODE [LF].)

  • Stop vehicle and access ON BOARD READINESS TEST to inspect DRIVE MODE completion status.

  • Verify FUEL_EVAL and EGR_EVAL PIDs status.

  • Does FUEL_EVAL and EGR_EVAL PIDs change to Yes?

Yes

Go to the next step.

No

Retry this step.

9

VERIFY TROUBLESHOOTING OF DTC P0401 COMPLETED
  • Make sure to reconnect all disconnected connectors.

  • Access DIAGNOSTIC MONITORING TEST RESULTS.

    (See ON-BOARD DIAGNOSTIC TEST [LF].)

  • Verify TEST #10:31:83 (EGR pressure variation) value.

  • Is value within the specification?

Yes

Go to the next step.

No

Replace the PCM, then go to the next step.

(See PCM REMOVAL/INSTALLATION [LF].)

10

VERIFY AFTER REPAIR PROCEDURE

Yes

Go to the applicable DTC inspection.

(See DTC TABLE [LF].)

No

Troubleshooting completed.




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