Pcm Operating Modes

As input signals to PCM change, PCM adjusts its response to output devices. For example, 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 PCM responds to various input signals. There are two types of engine control operation: OPEN LOOP and CLOSED LOOP.

In open loop operation, PCM receives input signals and responds according to preset programming. Inputs from heated oxygen sensors are not monitored.

In closed loop operation, PCM monitors inputs from heated oxygen sensors. This input indicates to PCM whether or not calculated injector pulse width results in ideal air-fuel ratio of 14.7 parts air to 1 part fuel. By monitoring exhaust oxygen content through oxygen sensor, PCM can fine tune injector pulse width. Fine tuning injector pulse width allows PCM to achieve optimum fuel economy combined with low emissions.

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