What Is EGR Valve?

Exhaust Gas Recirculation Valve — recirculates a controlled portion of exhaust gas back into the engine cylinders to reduce combustion temperatures and NOx emissions.

The EGR system dilutes the intake charge with inert exhaust gas, which lowers peak combustion temperatures and reduces nitrogen oxide formation. EGR valves can stick open or closed due to carbon buildup. Common related codes include P0400-P0409.