EGR Monitor (if equipped)

The Powertrain Control Module (PCM) performs an on-board diagnostic check of EGR system.

The EGR monitor is used to test whether EGR system is operating within specifications. The diagnostic check activates only during selected engine/driving conditions. When conditions are met, EGR is turned off (solenoid energized) and O2S compensation control is monitored. Turning off EGR shifts air fuel (A/F) ratio in lean direction. The O2S data should indicate an increase in O2 concentration in combustion chamber when exhaust gases are no longer recirculated. While this test does not directly measure operation of EGR system, it can be inferred from shift in O2S data whether EGR system is operating correctly. Because O2S is being used, O2S must pass its test before EGR test. Also looks at EGR linear potentiometer for feedback.