Moreover, the ECU, or the engine control unit is the brain of the vehicle which is commonly used for controlling all the sensors and solenoids of the engine for their smooth functioning. Moreover, it is also known as an engine control module or ECM in modern cars. When the ECU of the car is failed, it will affect the performance of the engine and make it difficult to start it. The following slide defines the signs to determine the failed ECU in your Audi.