Exhaust Gas Recirculation: Description and Operation

PURPOSE
System recirculates metered portions of exhaust gas into intake manifold, lowering combustion temperatures and reducing formation of Oxides of Nitrogen (NOx).

OPERATION
Amount of exhaust gas recirculated varies from zero with cold engine, to a fixed rate for hot engine with intermediate load and low engine speed. Flow rate increases steadily as coolant temperature rises above 55°C (131°F). The system employs a control and vent solenoid, controlled by the Powertrain Control Module (PCM). The PCM will disable the EGR system under conditions of zero throttle opening, full throttle, low coolant temperature, low engine speed, transmission in neutral, or system malfunction.

EGR Solenoids
EGR valve operation is regulated by EGR Control (EGRC) and EGR Vent (EGRV) solenoid valves. When sensor inputs determine the EGR valve should open, the PCM energizes the EGRC solenoid, sending vacuum to open the EGR valve. To close the EGR valve the PCM de-energizes the EGRC solenoid and energizes the EGRV solenoid, venting vacuum from the EGR valve diaphragm until the desired position is reached.

EGR Valve Position Sensor
The EGR Valve Position (EVP) sensor detects EGR valve movement and signals the PCM. With this and other input information, the PCM modifies the EGR valve position for optimum emission control under a variety of operating conditions.