The EGR system is responsible for the exhaust and gas recirculation. Recalculating the exhaust gets the most out of the fuel. When the engine is cold it does not burn fuel efficiently. The EGR system recalculates this exhaust so that unused fuel can be used to its capacity. The EGR valve lets the exhaust into the system so it can be recalculated. It opens and closes with a vacuum that is activated by a solenoid. When the engine is cold, the valve is open so that the exhaust can be circulated again. As the engine warms up, the valve closes. It opens and closes depending upon the needs of the engine and how efficiently the fuel is being burned. Repairs to the EGR, in most cases, are quite accessible. There are lots of small parts that need to be removed and replaced in the process. Problems with the EGR may render the car simply inefficient or the engine may not work at all.