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. The manifold differential pressure sensor is located in the intake manifold plenum. This sensor detects variations in the manifold negative pressure when the EGR solenoid is momentarily operated. If the manifold negative pressure changes, the EGR system is normal. In normal vehicle operation performed after warming up of the engine, the EGR valve is opened to carry out EGR. The ECM uses this to check the operation of the EGR system. If a problem is found, the check engine/malfunction indicator light illuminates to warn the driver that a problem has occurred.