Electronic control unit (ECU) is a small device inside a vehicle that controls one or several electrical systems in that vehicle. It tells electrical systems what to do and how to operate. ECU’s core is a microcontroller and it is controlled by embedded software. To fulfil its purpose, ECU receives input from one or several parts of the vehicle. For example, an airbag ECU receives information from crash sensors and seat sensors. When there is a crash, the ECU decides which airbags to deploy depending on where passengers are sitting. Then it tells the actuators to deploy them. After that, the actuator converts the electrical signal into the physical value needed, using valves, injectors or relays.
Vehicles may contain over 100 ECUs that in addition to essential functions, like engine performance and power steering, control comfort and security features, such as parking assistance, memory seats and airbag deployment.