The electrical system:
Electricity powers most of the devices in the car. The starting motor requires electricity to crank the engine, the ignition system requires electricity to deliver spark inside the cylinders. The fuel injectioin system, lights, horns, radio, air conditioner and other accessories require electricity to operate. The battery supplies electricity while the engine is off and for cranking the engine. After the engine starts, the alternator recharges the battery and supplies power for the electrical load.
The electronic control systems:
Many devices and systems on the car require a control system for safe and proper operation. A basic control system has three parts. These are inputs, the control unit and the outputs. The inputs are switches and sensors; they provide information to electronic control modules (ECM). Then the ECM signals the output devices or actuators to take the required action. The ECM has a self-diagnostic capability. This means a memory stores information about faults or malfunctions that have occurred and perhaps disappeared. When recalled from the memory this stored information helps the technician to diagnose and repair the vehicle.