P0401

Test 1:

Tests 2 - 6:

Tests 7 - 11:

Tests 12 - 14:

SYMPTOM
P0401 - EGR SYSTEM FAILURE

WHEN MONITORED
With engine temp greater than 82 °C (180 °F) ambient temperature above -18 °C (0 °F), engine in closed loop, 02 sensor operational, engine under a steady load with the throttle open, and 02 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
- Inspect EGR assembly
- EGR valve open at idle
- Wiring harness intermittent problem
- ASD relay output circuit open
- EGR solenoid control circuit open
- EGR Solenoid control circuit short to ground
- EGR solenoid control circuit shorted to sensor ground
- EGR solenoid control circuit shorted to voltage
- PCM
- PCM open internally
- PCM shorted internally