Exhaust Gas Recirculation: Description and Operation

Exhaust Gas Recirculation (EGR) System:

GENERAL DESCRIPTION
The Exhaust Gas Recirculation (EGR) system controls the formation of Oxides of Nitrogen (NOx) emissions by recirculating the exhaust gases into the combustion chamber. This is done through the intake manifold.

OPERATION
The EGR system is controlled by the Powertrain Control Module through the Exhaust Gas Recirculation Solenoid Vacuum (EGR SV) valve and EGR pressure transducer.

A diaphragm mounted in the EGR pressure transducer is operated by back pressure of the exhaust gas to open and close the valve. By this opening and closing action of the valve, the EGR pressure transducer controls the vacuum transmitted to the EGR valve.

Under a low load condition such as low speed driving, the exhaust pressure is low. In this state, the diaphragm in the EGR pressure transducer is pushed down by the spring force and the pressure transducer valve opens to allow the air into the vacuum passage from the outside.

As a result, less vacuum is transmitted to the EGR valve because it has been partially vented.

Therefore, the EGR valve is not pulled fully open and less exhaust gas is recirculated to the intake manifold.

Under a high load condition such as high speed driving, the exhaust pressure is high. By the high exhaust pressure, the diaphragm in the pressure transducer is pushed up and closes its valve. As the air does not enter the vacuum passage in this state, the vacuum transmitted to the EGR valve grows larger and so does the opening of the EGR valve. Thus, a larger amount of exhaust gas is recirculated to the intake manifold.

Under any of the following conditions, the PCM closes the vacuum passage of EGR SV valve. In this state, as the vacuum is not transmitted to the EGR valve, it remains closed.

^ When the Engine Coolant Temperature sensor is low.
^ When the throttle valve is at the idle position.
^ When the engine is running under high load.
^ When the intake manifold pressure is low.

Other than the above, the EGR valve opens and closes in accordance with the EGR pressure transducer.

The PCM activates the EGR Bypass Valve only when it diagnosis the EGR system.