Exhaust Gas Recirculation: Description and Operation

EGR System Input/Output Signal Line:

Fig. 145 Vacuum Solenoid:

PURPOSE
The Exhaust Gas Recirculation ( EGR ) System controls 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.

OPERATION
The EGR valve is controlled by the Engine Control Module (ECM) through the EGR solenoid.

If the ECM senses:
^ Low engine coolant temperature
^ Engine cranking
^ Engine speed over 2700 rpm
^ Engine idling
^ Excessively high coolant temperature
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.