A powertrain control module (PCM) is the "brains" of your car. It is basically a printed circuit board computer that sends electronic signals to all of the different components in the engine, and tests the temperature and airflow around them, to check on the status of their operation. The control module examines the camshaft, coolant levels, crankshaft, ignition and valve timing, air intake and the turbocharger components in a car. It automatically regulates the ratio of air to fuel used in the engine and controls the idle speed so that the vehicle operates at peak performance levels. The module also works in conjunction with the catalytic converter to reduce the amount of pollutants expelled with the engine's exhaust and maintains the speed of the vehicle when the cruise control feature is turned on.