The Power Train Control Module or PCM (for its acronym in English Powertrain Control Module) is a control unit that is combined with the ECM (Engine Control module) and the TCM (Transmission Control Module).
The PCM has primary inputs which come from many sensors, which vary in their type and are distributed throughout the vehicle. The sensors help the good operation of the vehicle and that the performance of the engine is the most effective.
In the case of the PCM (Powertrain Control Module) it controls more than 100 factors in the car. One of its functions is that it can show hundreds of error codes which indicate a problem in the vehicle. Usually, when one of these errors occurs, the check engine light or "check the engine" lights up on the dashboard. We could say that the Power Train Control Module is the brain of the motor control system, since it collects information from all available means, then processes and uses said data to make decisions regarding the operation of your motor of your vehicle.
Over time this control system has taken greater possession in most vehicles, to mention: the position of the accelerator, the position of the crankshaft, and the air pressure in the manifold, oxygen sensors, detonation, among others. In addition to, processors that are fast and allow adjusting the fuel injection, as well as the ignition timing and thus optimizing any variable. The Powertrain Control Module controls all the functions of the vehicle, along with the functions of the engine, controls the functions of the automatic transmission, such as the automatic change when the vehicle accelerates or when the vehicle must lower the change at the moment when the slows down.