EGR Valve: Description and Operation

Linear EGR Valve:

Internal View:

The Exhaust Gas Recirculation (EGR) system lowers the Oxides of Nitrogen (NOx) emission levels caused by high combustion temperatures.To decrease combustion temperatures, the linear EGR valve feeds small amounts of exhaust gas back into the combustion chamber. The exhaust gases combine with the incoming air/fuel mixture to lower combustion temperatures.

Operation
The linear EGR valve supplies exhaust gas recirculation (EGR) to an engine independent of intake manifold vacuum. The PCM controls recirculation flow from the exhaust, through an orifice, and into the intake manifold by the linear EGR valve pintle. During operation, the PCM controls pintle position by monitoring the pintle position feedback signal. The feedback signal can be monitored with a scan tool as ACTUAL EGR POS. In normal operation, ACTUAL EGR POS should always be near the commanded EGR position ( DESIRED EGR POS). The PCM uses information from the following sensors to control the pintle position:
^ Engine Coolant Temperature (ECT) sensor.
^ Throttle Position (TP) sensor.
^ Mass Air Flow (MAF).
The linear EGR valve is usually activated under the following conditions:
^ Warm engine operation
^ Above idle speed