Modes Of Operation

WARNING: This page is about a different car, the 1995 Plymouth Voyager, 1995 Plymouth Grand Voyager, 1995 Dodge Grand Caravan, and 1995 Dodge Caravan. However, it is still accessible from the selected car via links, so may be relevant.

As input signals to PCM change, PCM adjusts its response to output devices. Modes of operation come in 2 types, open loop and closed loop. In open loop mode, PCM is not using input from oxygen sensor to adjust fuel mixture. In open loop mixture and timing may be fixed or following a pre-programmed profile.

In closed loop mode, PCM is adjusting ignition timing and using input from oxygen sensor to fine tune injector pulse width.

The following inputs are used to determine PCM mode:

A/C Control Positions
A/C Switch
Battery Voltage
Brake Switch
Camshaft Position Sensor
Coolant Temperature Sensor (CTS)
Crankshaft Position Sensor
Engine Speed
Park/Neutral Position Switch
Idle Contact Switch
Manifold Absolute Pressure (MAP) Sensor
Heated Oxygen Sensor (HO2S)
Starter Relay
Throttle Position Sensor (TPS)

From these inputs, PCM determines which mode vehicle is in and responds appropriately. Not all inputs are used in all modes or by all models. Modes of operation are:

Ignition Switch In ON Position (Zero RPM)

When ignition switch is in ON position and PCM does not detect a crankshaft position signal (distributor signal), PCM will de-energize Automatic Shutdown (ASD) Relay. When ASD relay is not energized, battery power is cut from fuel injectors, fuel pump and coil.

Engine Start-Up

This is an open loop mode. When starter is engaged, PCM receives distributor signal and energizes Auto Shutdown (ASD) relay. Once ASD relay is energized, PCM determines proper injector pulse width and ignition timing from input signals. During engine start-up, PCM energizes all injector(s) simultaneously until it determines crankshaft position.

Engine Warm-Up

This is an open loop mode. PCM determines injector pulse width using information from various inputs and controls each injector sequence and pulse width. PCM controls engine idle speed, throttle stop angle and ignition timing.

Cruise Or Idle

When engine is at operating temperature, system is in closed loop mode. Using information from various inputs, PCM determines injector pulse width. PCM controls engine idle speed (using IAC motor), throttle stop angle and ignition timing. PCM determines proper air/fuel ratio using input from oxygen sensor(s).

Acceleration

This is a closed loop mode on all FWD models. All other models are in open loop mode. When PCM recognizes an abrupt increase in throttle position or MAP pressure as a demand for increased engine output, it increases injector pulse width in response to increased fuel demand.

Deceleration

This is a closed loop mode. When PCM receives inputs signaling a closed throttle and an abrupt decrease in manifold pressure, a hard deceleration is indicated. PCM may reduce injector firing to one pulse per engine revolution to lean air/fuel mixture. PCM also prevents EGR and EVAP purge functions during deceleration by grounding EGR and EVAP purge solenoids. PCM may cycle air switching solenoid for short periods of time in response to a high vacuum signal from MAP sensor.

Wide Open Throttle (WOT)

This is an open loop mode. When PCM senses wide open throttle, it grounds EGR and EVAP purge solenoids to prevent EGR and EVAP purge functions. Oxygen sensor input is not utilized and PCM adjusts injector pulse width to supply a predetermined amount of additional fuel.