Diagnostic procedure

WARNING: This page is about a different car, the 2005 Mazda 6. However, it is still accessible from the selected car via links, so may be relevant.

DTC P0401 [AJ] 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 related) been recorded?	Yes	Go to the next step.
1		No	Record FREEZE FRAME DATA and DIAGNOSTIC MONITORING TEST RESULTS on repair order, then go to the next step.
2	VERIFY RELATED REPAIR INFORMATION AVAILABILITY Check for related Service Bulletins and/or online 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.
2		No	Go to the next step.
3	INSPECT FOR OTHER DTCs Turn ignition switch to OFF then ON (Engine off). Have other DTCs been stored?	Yes	Repair circuit malfunction for applicable DTCs. (See DTC TABLE .)
3		No	Go to the next step.
4	INSPECT VACUUM HOSE CONDITION Inspect vacuum hoses for clogs, damage, freezing, or vacuum leakage. Is there any malfunction?	Yes	Replace vacuum hoses, then go to Step 9.
4		No	Go to the next step.
5	INSPECT EGR VALVE Inspect EGR valve. (See EGR VALVE INSPECTION [AJ] .) Is there any malfunction?	Yes	Replace EGR valve, then go to Step 9. (See EGR VALVE REMOVAL/INSTALLATION [AJ] .)
5		No	Go to the next step.
6	INSPECT EGR BOOST SENSOR Inspect EGR boost sensor. (See EGR BOOST SENSOR INSPECTION .) Is there any malfunction?	Yes	Replace EGR boost sensor, then go to Step 9.
6		No	Go to the next step.
7	INSPECT EGR BOOST SENSOR SOLENOID VALVE Inspect EGR boost sensor solenoid valve. (See EGR BOOST SENSOR SOLENOID VALVE INSPECTION [AJ] .) Is there any malfunction?	Yes	Replace EGR boost sensor solenoid valve, then go to Step 9.
7		No	Go to the next step.
8	INSPECT EGR VALVE GASKET Turn the ignition switch off. Remove EGR valve. (See EGR VALVE REMOVAL/INSTALLATION [AJ] .) Is EGR valve gasket normal?	Yes	Go to the next step.
8		No	Replace EGR valve gasket, then go to the next step. (See EGR VALVE REMOVAL/INSTALLATION [AJ] .)
9	MONITOR EGR SYSTEM BY DRIVE MODE Clear the DTC from the PCM memory using the WDS or equivalent. Run Drive Mode 1 (See OBD-II DRIVE MODE .) Stop vehicle and access ON BOARD READINESS TEST to inspect DRIVE MODE completion status. Verify FUEL_EVAL PID status. Does FUEL_EVAL PID change to Yes?	Yes	Retry this step.
9		No	Go to the next step.
10	MONITOR EGR SYSTEM BY DRIVE MODE Run Drive Mode 2. (See OBD-II DRIVE MODE .) Stop vehicle and access ON BOARD SYSTEM READINESS TEST to input DRIVE MODE completion status. Verify EGR_EVAL PID status. Does EGR_EVAL PID change to Yes?	Yes	Go to the next step.
10		No	Retry this step.
11	VERIFY TROUBLESHOOTING OF DTC P0401 COMPLETED Make sure to reconnect all disconnected connectors. Access DIAGNOSTIC MONITORING TEST RESULTS (Mode 6). (See DIAGNOSTIC MONITORING TEST RESULTS .) Verify TEST # 10: 31: 83 (EGR pressure variation) value. Is value within specification?	Yes	Go to the next step.
11		No	Replace PCM, then go to the next step. (See PCM REMOVAL/INSTALLATION .)
12	VERIFY AFTER REPAIR PROCEDURE Perform "AFTER REPAIR PROCEDURE". (See AFTER REPAIR PROCEDURE .) Are any DTCs present?	Yes	Go to the applicable DTC inspection. (See DTC TABLE .)
12		No	Troubleshooting completed.