DTC P0401: EGR System Failure: Description

System is monitored when engine coolant temperature is more than 180°F (82°C), ambient temperature more than 89°F (37°C), engine in closed loop, O2 sensor operational, engine under a steady load with throttle open and O2 controller not at or near its limits. O2 sensor signal is monitored for changes in its output during this test. DTC will set when PCM senses no change or too much change in O2 sensor signal. Possible causes are: defective EGR solenoid, EGR valve open at idle, Automatic Shutdown (ASD) relay circuit open, EGR solenoid control circuit open or shorted, or defective PCM.