P0401-EGR SYSTEM PERFORMANCE (CONTINUED)
For the Engine circuit diagram (Refer to 9 - ENGINE - SCHEMATICS AND DIAGRAMS).
For a complete wiring diagram Refer to Section 8W.
Theory of Operation
Exhaust gas recirculation is a method of reducing emissions of oxides of nitrogen. As the inert exhaust gas is recir-
culated, the mixture absorbs heat in the combustion chamber without interacting with the fuel/air mixture and
reduces the formation of NOx emissions. After the EGR monitor conditions are met, the EGR valve is turned on and
off momentarily. The EGR monitor calculated the difference in engine roughness from the EGR off condition to the
EGR condition. This engine combustion stability difference as measured by engine roughness is the measure of a
functional EGR system.
•
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 -6°C (20°F).
•
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 sig-
nal in the open state. A fueling sample is again established. The PCM then compares the different O2 Sensor
signal readings (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
(Z958) EGR SOLENOID GROUND CIRCUIT OPEN
(K35) EGR SOLENOID CONTROL CIRCUIT SHORTED TO GROUND
(K35) EGR SOLENOID CONTROL CIRCUIT SHORTED TO BATTERY VOLTAGE
(K35) EGR SOLENOID CONTROL CIRCUIT OPEN
EGR SOLENOID ASSEMBLY
PCM
Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. (Refer to 9 - ENGINE -
DIAGNOSIS AND TESTING).
Diagnostic Test
1.
ACTIVE DTC
Ignition on, engine not running.
With a scan tool, read DTCs.
Is the DTC active at this time?
Yes
>> Go To 2
No
>> Refer to the INTERMITTENT CONDITION Diagnostic Procedure.
Perform POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)
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ENGINE ELECTRICAL DIAGNOSTICS
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