DTC P0401: Exhaust Gas Recirculation (EGR) Flow Insufficient Detected

WARNING: This page does not describe the selected car, but rather 32 other vehicles, including the 2005 Mercury Sable, 2005 Mercury Mountaineer, 2005 Mercury Monterey, 2005 Mercury Montego, and 2005 Mercury Mariner. However, it is still accessible from the selected car via links, so may be relevant.

P0401 - EXHAUST GAS RECIRCULATION (EGR) FLOW INSUFFICIENT DETECTED

Description:	The EGR system is monitored during steady state driving conditions while the EGR is commanded on. The test fails when the signal from the differential pressure feedback EGR (DPFEGR) sensor indicates that EGR flow is less than the desired minimum.
Possible Causes:	Vacuum supply EGR valve stuck closed EGR valve leaks vacuum EGR flow path restricted EGRVR circuit shorted to PWR VREF open to DPFEGR sensor DPFEGR sensor downstream hose is off or plugged EGRVR circuit open to the PCM VPWR open to EGRVR solenoid DPFEGR sensor hoses are both off DPFEGR sensor hoses are reversed Damaged EGR orifice tube Damaged EGRVR solenoid
Diagnostic Acids:	Carry out the key on engine running (KOER) self-test and look for DTC P1408 as an indication of a hard fault. If P1408 is not present, look for contamination, restrictions, leaks, and intermittent faults.
Application	Key On Engine Off	Key On Engine Running	Continuous Memory
Vehicles with an EGR system module (ESM)	-	-	GO to HH: Exhaust Gas Recirculation System Module (ESM) STEP HH15.
All others	-	-	GO to HE: Exhaust Gas Recirculation (EGR) Systems STEP HE36.