2000 Ford Mustang

70) Continuous Memory DTC P0401: Perform KOER Self-Test

This DTC indicates EGR MONITOR failed due to PCM detecting EGR flow while driving is less than desired minimum. Possible causes for this fault are:
EGR valve stuck closed.
EGR valve diaphragm leak.
EGR flow plugged or restricted.
Faulty EGR hose.
EVR VPWR Circuit Open
EVR VPWR Circuit To PCM Open Or Shorted To PWR
DPFEGR Sensor VPWR Circuit Open
Faulty DPFEGR Sensor Hoses
Faulty DPFEGR Sensor
Faulty EGRVR Solenoid
Faulty PCM
If fault is currently present, KOER DTC P1408 should be present. Perform KOER ON-DEMAND SELF-TEST. If DTC P1408 is present, go to next step. If DTC P1408 is not present, go to step 90).