Exhaust Gas Recirculation: Description and Operation

PURPOSE
The exhaust gas recirculation (EGR) system lowers the nitrogen oxide (NOx) emission level. When the air/fuel mixture combustion temperature is high, a large quantity of nitrogen oxides (NOx) is generated in the combustion chamber. Therefore, this system recirculates part of emission gas from the exhaust port of the cylinder head to the combustion chamber through the intake manifold to decrease the air/fuel mixture combustion temperature, resulting in reduction of NOx. The EGR flow rate is controlled by the EGR valve so as not to decrease the driveability.

OPERATION
When the engine coolant temperature is low, when the engine is at idle or when a wide open throttle operation is performed, the EGR valve is kept closed, achieving no EGR. In normal vehicle operation performed after warming up of the engine, the EGR valve is opened to carry out EGR.

The EGR valve is provided with the EGR temperature sensor. If the engine control module detects low EGR gas temperature (EGR) gas temperature is low if the EGR valve is kept closed) during normal vehicle operation performed after warming up the engine, the engine control module turns on the check engine/malfunction indicator light to notify the driver that a failure has occurred in the EGR system.