PCM Operating Mode

PCM OPERATING MODES
As input signals to the Powertrain Control Module (PCM) change, the PCM adjusts its response to output devices. For example, the PCM must calculate a different injector pulse width and ignition timing for idle than it does for wide open throttle. There are several different modes of operation that determine how the PCM responds to the various input signals.

NOTE: There are two types of engine control operation: open loop and closed loop.

Open Loop
The PCM receives input signals and responds according to preset programming. Input from the heated oxygen sensor is not monitored.

Closed Loop
The PCM monitors the inputs from the heated oxygen sensor. This input indicates to the PCM whether or not the calculated injector pulse width results in the ideal air fuel ratio. By monitoring the exhaust oxygen content through the oxygen sensor, the PCM can fine tune injector pulse width. Fine tuning injector pulse width allows the PCM to achieve optimum fuel economy combined with low emissions.

NOTE: The engine start-up (crank) and engine warm-up modes are open loop modes. Under most operating conditions, the acceleration, deceleration, idle, and cruise modes, with the engine at operating temperature, are closed loop modes.