EGR System: Operation: Notes
A backpressure type EGR system is used on all engines. The backpressure transducer measures the amount of exhaust backpressure and varies the strength of the vacuum signal to the EGR valve. The signal vacuum is bled off into the atmosphere when exhaust backpressure to the EGR drops below a calibrated value.
On California models, the on-board diagnostic system checks the entire EGR system for failures. The system is activated and monitored only during selected driving conditions to avoid misdiagnosis. When monitored, the EGR solenoid is energized and EGR function will discontinue.
The Oxygen (O2) feedback system is monitored to see if a change occurs. The mixture should go lean and the system will try to enrich the mixture. The Single Module Engine Controller (SMEC) monitors EGR system performance and registers a fault code if the system has become less effective or has failed, and turns on the "CHECK ENGINE" light.