The engine control unit (ECU) is a small computer, i.e., a microprocessor, which controls the car's engine by evaluating data from various inputs (sensors) in real-time using specific software.

It is also equipped with a memory for storing certain types of data, for example, error codes, which can later be read using car diagnostics. One might say that the engine control unit is the car's brain.

Car diagnostics can detect several important pieces of information about the vehicle. Today, it is hard to find a car not equipped with an engine control unit (ECU / ECM). It is a microprocessor (or simply a small computer) that evaluates and stores a whole range of information.

The warning light on the dashboard then alerts the driver of a problem identified by the ECU. Though the illuminated warning light won't tell you much, to get detailed information about the problem, we need to access the car's database (memory) through car diagnostics.