P0401 EGR System Failure

SYMPTOM
P-0401 EGR SYSTEM FAILURE

WHEN MONITORED
With engine temp > than 180 degrees F; ambient temp> 0 degrees F, engine in closed loop, 02 Sensor operational, engine under a steady load with throttle open, and 02 Controller not at or near its limits.

SET CONDITION
If all conditions met, turn EGR off & on. 02 sensor signal is monitored for change in output signal. If no major change or too much change, flag is set. Repeat test up to 3x in run cycle (2 trips). If fails every time, code sets. If any pass, diagnostics are suspended.

POSSIBLE CAUSES
- Exhaust leak
- Intake manifold restricted
- EGR back pressure transducer defective
- EGR valve assembly defective
- EGR valve assembly mounted incorrectly
- EGR system failure does not reoccur
- EGR transducer line blocked
- EGR valve assembly diaphragm defective
- Vacuum supply to EGR solenoid inadequate