Modes Of Operation

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 (WOT). There are several different modes of operation that determine how PCM responds to various input signals.

There are two different areas of operation, OPEN LOOP and CLOSED LOOP. During OPEN LOOP modes PCM receives input signals and responds according to preset PCM programming. Inputs from upstream and downstream heated oxygen sensors are not monitored during OPEN LOOP modes, except for heated oxygen sensor diagnostics (they are checked for shorted conditions at all times).

During CLOSED LOOP modes PCM monitors inputs from upstream and downstream heated oxygen sensors. The upstream heated oxygen sensor input tells PCM if calculated injector pulse width resulted in ideal air-fuel ratio of 14.7:1. By monitoring exhaust oxygen content through upstream heated 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.

For PCM to enter CLOSED LOOP operation, the following must occur:

1. Engine coolant temperature must be over 35°F.
   • If coolant is over 35°F PCM will wait 44 seconds.
   • If coolant is over 50°F PCM will wait 38 seconds.
   • If coolant is over 167°F PCM will wait 11 seconds.
2. For other temperatures PCM will interpolate correct waiting time.
3. O2 sensor must read either greater than .745 volts or less than .2 volt.
4. The multiport fuel injection systems has following modes of operation:
   • Ignition Switch ON (Zero RPM)
   • Engine Start-Up
   • Engine Warm-Up
   • Cruise
   • Idle
   • Acceleration
   • Deceleration
   • Wide Open Throttle
   • Ignition Switch OFF
5. The engine start-up (crank), engine warm-up, deceleration with fuel shutoff and wide open throttle modes are OPEN LOOP modes. Under most operating conditions, acceleration, deceleration (with A/C on), idle and cruise modes, with engine at operating temperature are CLOSED LOOP modes.