Modern vehicles are equipped with control units (ECUs). In addition to the engine control unit, which controls, among other things, the injection and ignition, in most cases there are dozens of other control units, each with its own function. Examples include an ECU for the automatic transmission, the climate control, the lighting and signaling system, but also each door, which is equipped with its own ECU.
The interface electronics in the ECU convert the incoming sensor signals into a digital message. The processor reads this digital message and processes it in the memory. The processor executes instructions, comparing the data in the memories and generating an output. From a map, for example, the timing for fuel injection and ignition is determined based on the incoming sensor information (such as accelerator pedal position, vacuum in the intake manifold, engine speed and temperature). The process control provides feedback to adjust the process: when too much fuel has been injected, this is measured and fed back to the ECU, and the injection duration is reduced by means of the fuel trims.