The automotive sector is constantly and rapidly upgrading and deploying advanced features intocontemporary vehicles. To integrate these advanced features, numerous electronic systems are needed. Several controlmodules are used for enabling these systems to act jointly. Engine Control Module is a crucial part of vehicle’s EngineManagement System (EMS). Expanding interest for progressively controlled security features, traveler comfort, andoperational ease in vehicles requires an exhaustive utilization of electronic control units (ECU). The Engine ControlModule (ECM) provides the brains for the engine of the vehicle. It controls the fuel mixture; timing and emissionscontrol system and variety of other systems and sensors. This paper presents a review on ECU, different types ofcontrol units in vehicle, automotive communication protocols and working of an ECU.