Exhaust Gas Recirculation is a system designed primarily to reduce nitrogen oxide emissions from internal combustion engines, but a quality EGR system properly fitted can also increase engine efficiency. EGR is a required feature on most modern internal combustion engines. EGR works by recirculating a portion of an engine’s exhaust stream back in to the engine, optimising the incoming flow of oxygen and providing inert gasses that absorb some of the heat generated by the combustion process. Because EGR is now a legal requirement, faulty EGR systems will need to be replaced as soon as possible. In most modern vehicles, a damaged EGR will trigger a warning light on the dashboard and can cause the vehicle to fail an emissions test if checked.