Exhaust Gas RECIRCULATION: Notes

To lower oxides of nitrogen (NOx) exhaust gas emissions, an Exhaust Gas Recirculation (EGR) system is used. The EGR system introduces exhaust gases into intake system. Exhaust gases are noncombustible gases which, when combined with the incoming air/fuel mixture, lower peak combustion chamber temperatures.

The EGR valve receives ported operating vacuum from an ECM regulated EGR Vacuum Switching Valve (VSV). Various inputs to ECM are used to determine EGR operation. On California Prizm, Storm and Tracker models, EGR valve operation is monitored by ECM through signal from EGR temperature sensor. The EGR temperature sensor monitors exhaust gas temperature. If abnormal temperature exists, CHECK ENGINE light will be activated. On all models, vacuum signal to EGR valve is further controlled by a vacuum modulator located in the vacuum line between the EGR VSV and ported vacuum supply. Under low driving speeds and light load conditions, vacuum modulator diaphragm is pushed downward and opens vacuum modulator. This allows air to enter modulator from the outside, reducing vacuum supply to EGR valve. The EGR valve closes slightly, reducing amount of recirculated exhaust gases. Under high driving speeds and heavy load conditions, vacuum modulator diaphragm is pushed upward, closing vacuum modulator. This increases vacuum supply to EGR valve and valve opens slightly, increasing amount of recirculated exhaust gases. Under following conditions, ECM does not allow EGR operation:

• Coolant temperature is low
• Engine is operating under heavy load
• Engine speed exceeds 6000 RPM (Tracker)
• Low intake manifold pressure
• Mass airflow sensor reading is low (Prizm GSi)
• Throttle valve is at idle position
• A/T in lock-up condition (Federal Tracker Models)