Exhaust Gas Recirculation: Description and Operation

EGR OPERATION

Exhaust gas recirculation is used to reduce oxides of nitrogen emissions in the vehicle exhaust. EGR uses partial recirculation of exhaust gases from a port in the cylinder head to a port in the intake manifold. The EGR valve controls the flow of exhaust gas in response to ported vacuum. At partial throttle settings ported vacuum is high and the EGR valve is open. At full throttle and idle port vacuum is low and the EGR valve remains closed.

Fig. 45 Complete Emission Control System Diagram (Federal):

FEDERAL VEHICLES

Federal vehicles use a thermo valve to prevent EGR operation until the engine has reached operating temperature.

Fig. 46 Complete Emission Control System Diagram (California):

CALIFORNIA VEHICLES

California vehicles use an EGR solenoid valve controlled by the ECU to regulate operation of the EGR system and an EGR temperature sensor. The EGR temperature sensor allows the ECU to monitor operation of the EGR valve. If the temperature sensor output indicates that the EGR valve is malfunctioning the ECU will report the event with a fault code at the diagnostic connector.