Exhaust Gas Recirculation: Description and Operation

Exhaust Gas Recirculation (EGR) System Input And Output Chart:

Fig. 23 EGR Components:

PURPOSE

The EGR control system is used to allow precise control of the EGR valve to reduce the formation of NOx (Oxides of Nitrogen) emissions by recirculating some of the exhaust gases into the combustion chamber. The exhaust gas in the combustion chamber lowers the peak ignition temperature.

CIRCUIT OPERATION

When conditions are NOT suitable for EGR operation, based on signals sent via the crank angle sensor, air flow meter, engine temperature sensor and the ignition switch, the ECM energizes the solenoid. Refer to EMISSION CONTROLS for further description of the EGR valve.

EGR CONTROL SOLENOID

The EGR valve is controlled by the ECM through the EGR solenoid.

If the ECM senses:
^ Low engine coolant temperature
^ Excessively high coolant temperature
^ High engine speed
^ Engine idling
it energizes the EGR Control Solenoid. An energized solenoid will vent the vacuum signal and NOT allow EGR operation.

If the ECM senses any condition other than above, the EGR Solenoid will be de-energized and allow vacuum to pass.