Exhaust Gas Recirculation: Description and Operation

Description:

The Exhaust Gas Recirculation (EGR) system is used to lower Oxides of Nitrogen (NOx) emission levels caused by high combustion temperature. It does this by decreasing combustion temperature.

The main element of the system is the linear EGR valve. The EGR valve feeds small amounts of exhaust gas back into the combustion chamber. With the fuel/air mixture diluted by the exhaust gases, combustion temperatures are reduced.

Too much EGR flow at idle, cruise, or cold operation may cause any of the following conditions to occur:
^ Engine stalls after cold start.
^ Engine stalls during closed throttle conditions.
^ Vehicle surges during cruise.
^ Rough idle.
^ DTC P0300 (misfire detected).

Too little or no EGR flow may allow combustion temperatures to get too high. This could cause the following symptoms:
^ Spark knock (detonation).
^ Engine overheating.
^ Emission test failure.
^ DTC P0401.
^ Poor fuel economy.

EGR flow diagnosis is included in the DTC P0401 diagnostic table. Pintle position error and Control circuit diagnosis is covered in DTCs P0403, P0404, P0405 and P1404. If EGR diagnostic trouble codes are encountered, go to the DTC tables for diagnosis.