Exhaust Gas Recirculation: Description and Operation

The task of the Exhaust Gas Recirculation (EGR) is to regulate the fresh air supply to the engine by means of the exhaust gas recirculation system, in favor of clean combustion. The EGR system reduces oxides of nitrogen (NOx) in the engine exhaust. This is accomplished by allowing a predetermined amount of hot exhaust gas to recirculate and dilute the incoming charge air.

A malfunctioning EGR system can cause engine stumble, sags, or hesitation, rough idle, engine stalling and poor driveability.

The system consists of:
- A EGR valve assembly. The valve is located on the left side of the engine below the intake manifold.
- A EGR Cooler. The cooler is located on the left side of the engine below the intake manifold.
- A EGR air flow control valve. The EGR air flow control valve is located in the air inlet between the charge air inlet and the intake manifold. The air control valve is used to increase the EGR flow rate at low engine speeds.
- The ECM operates and monitors the EGR valve and air flow control valve.

The ECM is located in the left-rear side of the engine compartment. The ECM will monitor and determine the positioning of the EGR valve and air control valve by internal programming defined during engine development. This will depend on inputs from the engine coolant temperature, engine load, fuel quantity, throttle position and engine speed sensors. The air control valve blends the incoming charge air and the cooled and recirculated EGR gasses, to be used again in the combustion chamber.

Exhaust gas recirculation will begin in this order when:
- The ECM determines that EGR system operation is necessary.
- The inlet seat (poppet valve) at the bottom of the EGR valve opens to dilute and recirculate exhaust gas back into the intake manifold.
- The EGR Cooler further cools the hot exhaust gasses before recirculation

The EGR system will be shut down by the ECM after 60 seconds of continuous engine idling to improve idle quality and the air flow control valve will close completely when the vehicle is shut off to assist with engine shake on shut down.