Exhaust Gas Recirculation: Description and Operation

GENERAL INFORMATION
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 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
The EGR valve is being closed under one of the following conditions:

^ When the engine coolant temperature is low.
^ When the engine is at idle.
^ When the throttle valve is widely opened.

In order to recirculate exhaust gases, the EGR valve opens under the other conditions after warming up the engine.

In addition, the engine control module monitors the EGR system and illuminates the check engine/malfunction indicator light to let the driver know that there is a malfunction.