DTC P0401: EGR System Failure: Description

EGR system is monitored when engine temperature is 180°F (82°C), ambient temperature is more than 0°F (-18°C), engine is in closed loop, oxygen sensor is operational, engine is under a steady load with throttle open and oxygen sensor is not at or near its limits. DTC will set in Powertrain Control Module (PCM) memory when PCM detects too little or too much of a change in oxygen sensor output signal when EGR is turned off then on. Possible causes for DTC to set are: defective EGR valve, defective PCM, defective connectors or defective wiring.