EGR System

When vacuum is applied to diaphragm in EGR valve, EGR valve pintle opens, allowing exhaust gas to enter intake system. The level of vacuum that is applied to the EGR valve determines the volume of exhaust gas that enters the intake system.

To control this level of vacuum, a diaphragm in the EGR vacuum modulator responds to exhaust gas backpressure. As the diaphragm moves, it moves a valve that controls the level of vacuum that is applied to the EGR valve.

If the ECM detects one or more of the following conditions, it turns on the Vacuum Switching Valve (VSV), which shuts off the vacuum supply to the EGR valve:

• Engine coolant temperature is low
• Full deceleration has just occurred (throttle valve closed)
• Engine load is light (intake air volume is low)
• Engine speed is high.