Exhaust Gas Recirculation: Description and Operation

The Exhaust Gas Recirculation is regulated by the EGR Valve and controlled by a coolant temperature sensitive Thermo Valve. On California vehicles, an Exhaust Gas Temperature Sensor is mounted within the EGR valve. The sensor is used for detecting exhaust gas recirculation flow as an input to the ECU. If the EGR Valve should become stuck in the closed position, the sensor would not be able to reach its specified temperature, causing the MPI Control Unit to set a trouble code and illuminate the Malfunction Indicator Light. The same procedures would be followed if the temperature sensor were to malfunction.




The EGR Thermo Valve is normally open venting port vacuum back to the air intake. When the engine reaches operating temperature, the Thermo Valve closes and vacuum is applied to the EGR Valve, but additional vacuum will be required before the valve can open. The additional vacuum is supplied once the throttle is opened past the idle position, allowing exhaust gases to recirculate. When the throttle is fully opened (WOT.), the lack of port vacuum to the EGR Valve causes the EGR Valve spring to close the valve.