Exhaust Gas RECIRCULATION: Notes

The Exhaust Gas Recirculation (EGR) system is designed to reduce oxides of nitrogen (NOx) emissions by lowering combustion temperatures. This is accomplished when a metered amount of exhaust gas is recirculated into the intake manifold and mixed with the air/fuel mixture.

The 2 types of EGR systems used are pulse width modulated negative backpressure EGR using an EGR solenoid and either ported or manifold vacuum, and digital or linear EGR.

On PCM-controlled EGR systems using a solenoid, PCM controls ported or manifold vacuum to EGR valve through solenoid valve. Solenoid may be normally open or normally closed depending upon application.

PCM uses engine coolant temperature, throttle position and manifold pressure signals to determine vacuum solenoid operation. During cold engine operation and idle, EGR is not desired; therefore PCM causes solenoid to block vacuum to EGR valve. During warm engine operation and at speeds greater than idle, vacuum is allowed through solenoid, opening the EGR valve. To check EGR system, perform functional check of EGR system. See appropriate SYSTEM & COMPONENT TESTING article.