DTC P0401 [LF, L3]


DTC P0401	EGR flow insufficient detected
DETECTION CONDITION	• The PCM monitors the difference in intake manifold pressures when the EGR is operated and when it is stopped. If the difference is too small, the PCM determines that the EGR flow is insufficient. Diagnostic support note • This is an intermittent monitor (EGR). • The MIL illuminates if the PCM detects the above malfunction conditions in two consecutive drive cycles. • The DIAGNOSTIC MONITORING TEST RESULTS and PENDING CODE is available if the PCM detects the above malfunction condition during the first drive cycle. • The 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


STEP	INSPECTION		ACTION
1	PERFORM DTC CONFIRMATION PROCEDURE • Perform the DTC CONFIRMATION PROCEDURE. (See DTC CONFIRMATION PROCEDURE [LF, L3].) • Is the same DTC present?	Yes	Go to the next step.
1		No	Intermittent concern exists. Go to the INTERMITTNENT CONCERN TROUBLESHOOTING procedure. (See INTERMITTENT CONCERN TROUBLESHOOTING [LF, L3].)
2	INSPECT VACUUM HOSE CONDITION • Inspect the vacuum hoses for clogs, damage, freezing, or vacuum leakage. • Is there any malfunction?	Yes	Replace the vacuum hoses, then go to Step 6.
2		No	Go to the next step.
3	INSPECT EGR VALVE MALFUNCTION • Perform the EGR valve inspection. (See EGR VALVE INSPECTION [LF, L3]) • Is EGR valve normal?	Yes	Go to the next step.
3		No	Replace the EGR valve, then go to Step 6.
4	INSPECT MAP SENSOR MALFUNCTION • Perform the MAP sensor inspection. (See MANIFOLD ABSOLUTE PRESSURE (MAP) SENSOR INSPECTION [LF, L3]) • Is the EGR valve normal?	Yes	Go to the next step.
4		No	Replace the MAP sensor, then go to Step 6.
5	INSPECT EGR VALVE PASSAGE • Turn the ignition switch to the OFF position. • Remove the EGR valve. • Is the gasket installation normal?	Yes	Go to the next step.
5		No	Install the gasket correctly, then go to the next step.
6	MONITOR EGR SYSTEM BY DRIVE MODE • Clear the DTC from the PCM memory using the WDS or equivalent. • Run the PCM adaptive memory procedure drive mode. (See OBD DRIVE MODE [LF, L3].) • Access the RFC FLAG PID using the WDS or equivalent. • Is the RFC FLAG PID OFF?	Yes	Retry this step.
6		No	Go to the next step.
7	MONITOR EGR SYSTEM BY DRIVE MODE • Run the HO2S heater, HO2S, and the EGR system repair verification drive mode. (See OBD DRIVE MODE [LF, L3].) • Check if the EGR System Monitor is checked using the On-Board Readiness Test function. • Has the EGR system been monitored?	Yes	Go to the next step.
7		No	Retry this step.
8	VERIFY TROUBLESHOOTING OF DTC P0401 COMPLETED • Make sure to reconnect all disconnected connectors. • Access the DIAGNOSTIC MONITORING TEST RESULTS. (See Diagnostic Monitoring Test Results Access Procedure.) • Verify the TEST ID 10: 31: 83 value. • Is the value within the specification?	Yes	Go to the next step.
8		No	Replace the PCM, then go to the next step.
9	VERIFY AFTER REPAIR PROCEDURE • Perform the "After Repair Procedure". (See AFTER REPAIR PROCEDURE [LF, L3].) • Are any DTCs present?	Yes	Go to the applicable DTC inspection. (See DTC TABLE [LF, L3].)
9		No	Troubleshooting completed.