By rerouting exhaust gases from the exhaust into the intake, exhaust gas recirculation (EGR) valves can significantly reduce the emissions of nitrous oxides, known as NOx. NOx generation takes place in the combustion chamber at high temperatures. EGR valves introduce gases inert to combustion that absorb a part of the combustion heat, thus reducing the combustion temperature. Those valves can reroute the exhaust gases from the exhaust manifold upstream of the turbocharger (high-pressure EGR) or after the Diesel particulate filter (low-pressure EGR).

EGR valves efficiently reduce Nitrogen oxide emission. At preset load conditions, the valve lets in exhaust gas to the air intake, thereby adding less oxygen for combustion in the cylinders, thus lowering the temperature, which then reduces the formation of NOx.es