The Electronic Control Unit (ECU) is the electronic brain of a car's engine. It is typically situated in the engine compartment, close to the battery, near the glove compartment, or near the steering column of the passenger compartment. Some car manufacturers even place it underneath one of the seats. The fuel injector is a spray nozzle that supplies fuel to the engine. It is usually located in the combustion chamber, intake manifold, or throttle body.
All modern Electronic Fuel Injection (EFI) systems also have one or more detonation sensors, which are devices similar to microphones that detect a frequency range typical of abnormal combustion. When this frequency is detected, the ignition time is delayed in response. Nevertheless, this response may be false if different internal components of the engine alter the sound characteristics of the engine or external parts, such as exhaust systems, physically rub against the vehicle's chassis.