Exhaust Gas Recirculation: Description and Operation

The Exhaust Gas Recirculation (EGR) system controls Nitrous Oxide ((NOx) emissions. Metered amounts of exhaust gases are recirculated back into the combustion chamber to mix with the air/fuel charge. The combustion chamber temperature is reduced lowering NOx emissions.

The EGR system is enabled only during part throttle modes when the engine is warm and stabilized. The Throttle Position (TP) sensor indicates part throttle, and Engine Coolant Temperature (ECT) sensor indicates a warm engine. The Powertrain Control Module (PCM) controls EGR function necessary to avoid driveability concerns during idle and maximum power demands. The PCM compensates for changes in the air/fuel ratio when EGR gases are introduced.

Flow Diagram:

The EGR Valve Position (EVP) sensor is required in Electronic Engine Control (EEC) systems where EGR flow is controlled according to Powertrain Control Module (PCM) demands. As supply vacuum overcomes the spring load, the diaphragm is actuated. This lifts the pintle off its seat allowing exhaust gas to flow. The amount of flow is proportional to the pintle position. The EVP sensor mounted on the valve sends an electrical signal of its position to the PCM.


NOTE: Other vacuum related components may be incorporated into the EVP system, depending on vehicle model and Calibration.