Exhaust Gas Recirculation: Description and Operation

Digital EGR Circuit:

Digital EGR Valve:

Purpose:
The Exhaust Gas Recirculation (EGR) system is used to lower Oxides of Nitrogen (NOx) emission levels caused by high combustion temperature. It does this by reducing combustion temperatures.

The main element of the system is the digital EGR valve. The EGR valve feeds small amounts of exhaust gas back into the combustion chamber. With fuel/air mixture thus diluted, combustion temperatures are reduced.

Operation:
The digital EGR valve is designed to accurately supply EGR to an engine independent of intake manifold vacuum. The valve controls EGR flow from the exhaust to the intake manifold through three orifices which increment in size to produce seven combination. When a solenoid is energized, the armature, with attached shaft and swivel pintle is lifted, opening the orifice.

The flow accuracy is dependent on metering orifice size only, which results in improved control.

The digital EGR valve is usually activated under the following conditions:

^ Warm engine operation
^ Above idle speed

Digital EGR Control
The PCM regulates EGR flow by varying solenoid "ON/OFF" signals. The PCM uses information from the following sensors to regulate solenoid control:

^ Engine Coolant Temperature (ECT) sensor
^ Throttle Position (TP) sensor
^ Manifold Absolute Pressure (MAP) sensor

Location:
The EGR valve is located on the top right hand side of engine.