P0401

Tests 1 - 2:

Tests 3 - 7:

Tests 8 - 11:

SYMPTOM
P0401 - EGR SYSTEM FAILURE

WHEN MONITORED
With engine temp greater than 82 degrees C (180 degrees F) ambient temp above 32 degrees C (89 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
Conditions are met, the EGR is turned off and on momentarily. The oxygen sensor signal is monitor for changes in its output signal during this test. If no significant change or too much change is seen, a flag is set.

POSSIBLE CAUSES
- EGR solenoid
- EGR valve open at idle
- Wiring harness intermittent
- ASD relay output circuit open
- EGR solenoid control CKT open
- EGR solenoid control CKT short to GND
- EGR solenoid control CKT shorted to voltage
- PCM open internally
- PCM shorted internally