Exhaust Gas Recirculation: Description and Operation

EGR System Schematic:

PURPOSE AND OPERATION
The EGR function control system reduces oxides of nitrogen (NOx) emissions. Atmospheric oxygen and nitrogen do not normally combine except at very high temperatures and pressures. These conditions are present in the combustion chamber, especially during hard acceleration. When the engine is under load, the EGR valve admits a small amount of exhaust gas into the intake manifold to mix with the air/fuel charge. Exhaust gas is essentially inert and reduces peak combustion temperatures and pressures by absorbing some of the heat of combustion without participating in the actual burn. Greater amounts of exhaust gas are metered in as engine speed and load increase.

Primary EGR system components are: EGR control valve, EGR vacuum and vent solenoid valves, EGR function sensor, and the PCME.

EGR FUNCTION SENSOR
This sensor detects EGR control valve opening stroke and sends a signal to the PCME. The sensor is mounted on the EGR control valve.

EGR CONTROL VALVE
The EGR valve allows a portion of the exhaust gas into the intake manifold to reduce the amount of NOx produced by the engine.

EGR VACUUM AND VENT SOLENOID VALVES
The EGR vent and EGR vacuum solenoid valves control the vacuum signal to the EGR valve.

POWERTRAIN CONTROL MODULE
The PCME monitors signals from the crankshaft position sensors, air flow sensor, throttle position sensor, engine coolant temperature sensor, and EGR function sensor. It uses this information to determine when to operate the solenoid valves.