The Engine Control Module (also called the Powertrain Control Module or PCM) is the brains of the engine management system. It controls the fuel mixture, ignition timing, variable cam timing and emissions control. It constantly monitors emissions performance via its OBD (Onboard Diagnostics) programming, and it oversees the operation of the fuel pump, engine cooling fan and charging system. It also interacts with the transmission controller (if separate), ABS/traction/stability control system, body control module, climate control module and anti-theft system. In short, the engine control module performs a wide variety of functions that are necessary to operate a vehicle.