Most modern vehicles come complete with the so called "computer”, which is commonly known as ECU (electronic control unit).  This is a generic term for any embedded system that controls one or more of the electrical systems or subsystems in a motor vehicle.

There are several types of ECU, including Electronic/Engine Control Module (ECM), Powertrain Control Module (PCM), Transmission Control Module (TCM), Brake Control Module (BCM or EBCM), Central Control Module (CCM), Central Timing Module (CTM), General Electronic Module (GEM), Body Control Module (BCM), Suspension Control Module (SCM), control unit, or control module. Taken together, these systems are sometimes referred to as the car’s computer. (Technically there is no single computer but multiple ones.) Sometimes one assembly incorporates several of the individual control modules (PCM is often both engine and transmission).Some modern motor vehicles have up to 80 ECUs. Embedded software in ECUs continues to increase in line count, complexity, and sophistication. Managing the increasing complexity and number of ECUs in a vehicle has become a key challenge for original equipment manufacturers (OEMs).  Since there is no single control unit but a combination of several, there is a long list of ECUs and some of which may include several types of electronic control units, notably Airbag Control Unit (ACU), Body Control Module controls door locks, electric windows, courtesy lights, etc. Convenience Control Unit (CCU), Door Control Unit, Engine Control Unit (ECU) – not to be confused with electronic control unit, the generic term for all these devices though!Electric Power Steering Control Unit (PSCU)Generally this will be integrated into the EPS power-pack. Human Machine Interface (HMI), Powertrain Control Module (PCM): Sometimes the functions of the Engine Control Unit and Transmission Control Unit are combined into a single unit called the Powertrain Control Module.  Things like the Seat Control Unit, Speed Control Unit, Telephone Control Unit (TCU), Transmission Control Unit (TCU) and Brake Control Module (ABS or ESC) are some of the many ECUs on a number of vehicles. The more sophisticated the cars become, the more modules the manufacturers add!  That is why we say that there are no standard ECU functions that all vehicles must have – it all depends on the manufacturers and how they want their vehicles to behave!There are several thousand functions that the ECUs can perform or control, e.g. fuel intake, emissions, battery check, oil check, safety checks, etc.  All these have a particular code and it is such a code that would trigger an alert when the function for which it was programmed to monitor goes haywire! It is like a watchman seeing someone trying to take property out of a premise he is guarding; he would swing into action by either making an alarm or taking any other action that may impede the wrong action! In the same manner, the code will trigger an indicator or an audio alert or a combination of both, so that the driver can be alerted. If the driver is alerted and he does not take action, the ECU might decide to shut down the engine if it is in trouble of getting seriously damaged!The interpretation of the alerts in order to determine the exact problem is the role of experts that use a device specifically designed to read and interpret such codes. An OBD2 Scanner like OBDCOM is used.  This is a computer that is attached to a special socket (this socket is found on most vehicles manufactured from 1992 onwards), the computer reads the codes and is able to diagnose the exact faulty part. It is highly advisable for all motor vehicle owners to have their vehicles diagnosed periodically; this could save you from severe engine failures resulting from the failure of simple but important components.