EGR Valve: Description and Operation

Location:

Operation
The function of the Exhaust Gas Recirculation (EGR) system is to reduce emissions by recirculating exhaust gases back into the inlet manifold thus reducing peak combustion temperatures and NOx emissions.

The system comprises an EGR valve and transfer pipe. The EGR valve is fitted to the induction elbow which is located between the base of the throttle body and the induction manifold. The transfer pipe connects the RH exhaust manifold to the EGR valve.

The EGR valve contains a four pole (60 step) stepper motor which is driven by the ECM. The valve is cooled by the coolant return from the electronic throttle body

When the EGR system is not fitted, a blanking plate is bolted onto the induction elbow.

EGR Valve:

Monitoring Procedure
The ECM monitors the difference in air flow, from the MAFM, between the EGR valve being open and closed. The resultant change in air flow is monitored against a set value. Should the flow be outside the fixed parameters, a flow malfunction is flagged, using twin trip logic.

The stepper motor / circuit is monitored for low value, open circuit and high value short circuit and is also flagged on a twin trip logic.

In this application the SAE DTC definition for sensor refers to the stepper motor integrity.

Circuit Diagram, EGR System/Ecm: