Powertrain Control Module: Description
The Powertrain Control Module (PCM) is located in the engine compartment. See Fig 1 -Fig 3 . The PCM may also be referred to as Jeep/Truck Engine Controller (JTEC). As input signals to the PCM change, the PCM adjusts its response to the output devices. For example, the PCM must calculate different injector pulse width and ignition timing for idle than it does for Wide Open Throttle (WOT). The PCM will operate in two different modes: open Loop and Closed Loop. During Open Loop mode, the PCM receives input signals and responds only according to preset PCM programming. Input from the Oxygen (O2) sensors is not monitored during Open Loop mode. During Closed Loop mode, the PCM will monitor the O2 sensors input. This input indicates to the PCM whether or not the calculated injector pulse width results in the ideal air/fuel ratio. This ratio is 14.7 parts air-to-1 part fuel. By monitoring the exhaust oxygen content through the O2 sensors, the PCM can fine tune the injector pulse width. This is done to achieve optimum fuel economy combined with low emission engine performance. The fuel injection system has several operating modes. See MODES OF OPERATION under FUEL CONTROL under FUEL SYSTEMS.