Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Modes Of Operation: Notes
As input signals to the 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 (WOT). There are several different modes of operation that determine how the PCM responds to the various input signals.
The multi-port fuel injection systems has the 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
Within these modes of operation, there are two different types of operation, OPEN LOOP and CLOSED LOOP.
During OPEN LOOP operation the PCM receives input signals and responds according to preset PCM programming. Inputs from the upstream and downstream heated oxygen sensors are not monitored during OPEN LOOP operation, except for heated oxygen sensor diagnostics (they are checked for shorted conditions at all times).
During CLOSED LOOP operation the PCM monitors the inputs from the upstream and downstream heated oxygen sensors. The upstream heated oxygen sensor input tells the PCM if the calculated injector pulse width resulted in the ideal air-fuel ratio of 14.7 to one. By monitoring the exhaust oxygen content through the upstream heated 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.
For the PCM to enter CLOSED LOOP operation, the following must occur:
- Engine coolant temperature must be over 35°F (1.7°C).
- If the coolant is over 35°F (1.7°C) the PCM will wait 38 seconds.
- If the coolant is over 50°F (10°C) the PCM will wait 15 seconds.
- If the coolant is over 167°F (75°C) the PCM will wait 3 seconds.
- For other temperatures the PCM will interpolate the correct waiting time.
- O2 sensor must read either greater than 0.745 volts or less than 0.29 volt.
OPEN LOOP operation is used for engine start-up (crank), engine warm-up, deceleration with fuel shutoff and wide open throttle. Under most conditions, acceleration, deceleration (with A/C on), idle and cruise modes, with the engine at operating temperature occur in CLOSED LOOP operation.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.
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