Exhaust Gas Recirculation: Description and Operation

Purpose
Exhaust Gas Recirculation (EGR) reduces Oxides Of Nitrogen (NOx) emissions in the vehicle exhaust.

Operation
The EGR system injects a metered amount of exhaust gas into the intake manifold to lower the combustion temperature.
- Lower combustion temperatures reduce the formation of NOx.

When the Electronic Control Module (ECM) determines conditions are suitable for EGR operation it disconnects the ground supply to the solenoid--allowing ported manifold vacuum to be applied to the EGR valve diaphragm controlling the flow of exhaust gas.
- At partial throttle settings ported vacuum is high and the EGR valve is open.
- At full throttle and at idle ported vacuum is low and the EGR valve remains closed.

The EGR system is also equipped with a temperature sensor in the exhaust passage (for self-diagnostic purposes)--to signal the ECM when the EGR system is not operating properly.