EGR is a shortcut of Exhaust Gas Recirculation. The system is used in cars equipped with an internal combustion piston engine. It was designed to reduce pollutions in combustions gases. The main reason for putting through this solution was the growing number of toxic pollutants emitted by cars.

The EGR valve works by recirculating a measured amount of the exhaust gases back into the engine through the air intake system, reducing the amount of emissions the engine produces.

The problem lies with the exhaust gas that contains carbon deposits, this gas is constantly being recirculated through the engine, which over time will cause a build-up of the carbon deposits in the intake manifold and other parts including the EGR valve. This build up in the valve is often what causes them to fail.

The EGR Cooler is designed to lower the temperature of the exhaust gases before they are recirculated back into the engine. This is done to keep the inlet air temperatures as low as possible. These are known for cracking which normally results in coolant loss. Later model Engines have flaps and solenoids on the Coolers, as well as sensors to monitor its operation. When these fail, fault codes and warning lights may also be triggered.