A Chevy exhaust gas recirculation (EGR) valve is a necessary part of the car's emissions system. It works by rerouting some of the exhaust gases back into the intake manifold rather than into the atmosphere.
There are several types of EGR valves with the same function but different modes of operation. Older EGR valves are purely mechanical and run on vacuum; on many newer Chevrolet and other GM models, the valve is controlled entirely by computer. This type uses multiple solenoids to open the valve in response to input from the car's computer, opening and closing the valve to allow exhaust gas flow.
Whether the EGR valve uses vacuum or electronic control, it opens when exhaust gases reach a certain temperature or level of backpressure. When the EGR valve opens, some of the exhaust is rerouted to the intake manifold. Since it is less combustible than the air-fuel mixture in the manifold, the temperature drops.
The main function of an EGR valve is to lower the amount of nitrogen oxide a car releases into the atmosphere. A failed EGR valve prevents a car from passing emissions testing, if required. The valve's secondary function is to lower the temperature in the intake manifold.
