P0401

Tests 332 - 338:

Tests 339 - 340:

SYMPTOM
P-0401 EGR SYSTEM FAILURE

WHEN MONITORED
With engine temperature greater than 180 degrees F, ambient temperature above 0 degrees F, engine in closed loop, O2 Sensor operational, engine under a steady load with the throttle open, and O2 Controller not at or near its limits.

SET CONDITION
If all conditions met, turn EGR off & on. O2 Snsr Sig is monitored for change in output sig. 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, diags 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 diaphram defective
- Vacuum supply to EGR solenoid inadequate