EGR Valve: Description and Operation

DESCRIPTION
The EGR system is used to lower Oxides of Nitrogen (NOx) emission levels caused by high combustion temperatures and an abundance of oxygen. It does this by decreasing combustion temperature and replacing the oxygen with exhaust gas.

The main element of the system is the EGR valve operated by vacuum, and mounted on the intake manifold. The EGR valve feeds small amounts of exhaust gas back into the combustion chamber.

OPERATION
The EGR valve is opened by manifold vacuum and is regulated by an ECM controlled solenoid valve to let exhaust gas flow into the intake manifold. The exhaust gas then moves with the air/fuel mixture into the combustion chamber. If too much exhaust gas enters, combustion will not occur. For this reason, very little exhaust gas is allowed to pass through the valve, especially at idle. The EGR valve is usually open during warm engine operation and when the vehicle is above idle speed.