Exhaust Sensors and Valves

What is the purpose of the lambda sensor and the EGR valve?

All exhaust sensors have a regulating function onto the exhaust fumes. The most important one is the lambda sensor. Most cars have two lambda sensors close to the cat con. One is fixed in front and the other behind. The first sensor is only there to provide information whereas the second has a regulating function. The EGR valve has a similar purpose. The difference being though that this car part is located much closer to the engine. In addition the EGR valve helps the exhaust fumes to cool down before they are injected into the exhaust system.