Exhaust Gas Recirculation: Testing and Inspection

Exhaust Gas Recirculation (EGR) System Diagnosis






Circuit Description

The Exhaust Gas Recirculation (EGR) system lowers the Oxides of Nitrogen (NOx) emission levels created by the high combustion temperatures by suppling cooler exhaust gasses to the combustion chamber.

The EGR valve pintle is opened by the PCM when the conditions of operation have been met. The exhaust gas flows from the exhaust manifold through the EGR pipe, intake manifold passages, and the EGR valve orifice into the intake manifold. The exhaust gasses mix with the intake air and enters the combustion chamber.

Diagnostic Aids

Too little EGR flow or no EGR flow allows the combustion temperature to increase. This causes the following symptoms:

* Spark knock (detonation)
* Engine overheating
* Emission test failure
* Poor fuel economy

Restrictions or blockage in the EGR passages may be caused by the following conditions:

* Contaminated fuel
* Poor fuel quality
* High mileage or excessively worn internal engine components

Too much EGR flow causes any of the following conditions to occur:

* The engine stalls after a cold start
* The engine stalls during closed throttle condition
* A rough idle

Test Description

The numbers below refer to the step numbers on the diagnostic table.
2. DTC P0404, P0405, P1404 a problem in the EGR valve electrical circuits.

3. This test will determine if any EGR passages are restricted.