P0401

Test 1:

Test 2 - Test 6:

Test 7 - Test 11:

SYMPTOM
P0401 - EGR SYSTEM PERFORMANCE

WHEN MONITORED
Engine running for greater than two minutes with the Engine Coolant Temp greater than 70° C (158° F). EGR active. Less than 8500 feet. Ambient temperature greater than 20° F (-6° C)

SET CONDITION
The PCM closes the EGR valve while monitoring the O2 Sensor signal. Once a closed EGR fueling sample has been established the PCM then ramps in EGR and additional fueling while monitoring the O2 Sensor signal in the open state. A fueling sample is again established. The PCM then compares the two different O2 Sensor signal reading (fueling samples). If a larger than expected variation is detected, a soft failure is recorded. Three soft failures set a one trip failure. After two failed trips, a DTC is set and the MIL is illuminated.

POSSIBLE CAUSES
- Good trip equal to zero
- EGR valve open at idle
- EGR valve assembly inspection
- EGR solenoid assembly
- EGR solenoid ground circuit open
- EGR solenoid control CKT short to GND
- EGR solenoid control CKT shorted to voltage
- EGR solenoid control CKT open
- PCM - EGR open
- PCM - EGR closed