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

The following inputs are used to determine PCM mode.

Charge Temperature Sensor
Coolant Temperature Sensor (CTS)
Fuel Temperature Sensor
Fuel Low-Pressure Sensor
Idle Contact Switch
MAP Sensor
Engine Speed
Throttle Position (TP) Sensor
Gear Position
A/C Switch
Battery Voltage
Oxygen Sensor (O2S)
A/C Control Positions

From these inputs, PCM determines which mode vehicle is in and the appropriate response. Not all inputs are used in all modes. The 8 modes of operation are as follows:

Ignition Switch In ON Position

This is an open loop mode. PCM determines atmospheric pressure from MAP sensor and determines basic fuel strategy. PCM modifies fuel strategy according to ambient air temperature, coolant temperature, fuel temperature and fuel pressure inputs. PCM activates auto shutdown relay, which in turn activates low-pressure fuel shutoff solenoid and ignition circuit for approximately 2 seconds unless engine is cranked. PCM also activates CNG fuel shutoff solenoid relay, which in turn activates high-pressure fuel shutoff solenoid and O2S heater element for approximately 2 seconds unless engine is cranked.

Engine Start-Up

This is an open loop mode. When starter is engaged, PCM receives crankshaft position and 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 and sends a signal to fuel injector driver module to power up fuel injectors. PCM provides ground for injectors to fire in proper order. If PCM does not receive crankshaft position sensor signal within 3 seconds after engine begins cranking, fuel injection system is shut down and a fault code is set in PCM memory.

Engine Warm-Up

This is an open loop mode. PCM determines injector pulse width using information from battery voltage, crankshaft position sensor, coolant, charge and fuel temperature sensors, MAP sensor and distributor pick-up. PCM also monitors A/C request, fuel low-pressure sensor and Park/Neutral switch (if equipped) signals for fuel calculation. PCM controls engine idle speed and ignition timing.

Idle

This is an closed loop mode. In idle mode, PCM now adds O2S signal to the array of inputs. PCM maintains correct air/fuel ratio by adjusting injector pulse width and ignition timing. PCM also controls A/C clutch operation if A/C is requested.

Cruise

When engine is at operating temperature, this is a closed loop mode. Using information from various inputs, PCM determines injector pulse width and ignition timing under different engine load conditions. PCM determines proper air/fuel ratio using input from O2S.

Acceleration

This is an open loop mode. When PCM recognizes an abrupt increase in throttle position or manifold pressure as a demand for increased engine output, it increases injector pulse width through fuel injector driver module in response to increased fuel demand.

Deceleration

This is an open loop mode. When PCM receives inputs signaling a closed throttle and an abrupt decrease in manifold pressure, it reduces injector pulse width to lean air/fuel mixture. Under certain RPM and closed throttle position conditions, O2S signals are ignored and PCM cuts off fuel injection until idle speed is reached. PCM also drives AIS motor for smooth transition to idle mode.

Wide Open Throttle

This is an closed loop mode. When PCM senses wide open throttle, it grounds EGR and evaporative purge solenoids to prevent EGR and canister purge functions. Oxygen sensor input is ignored and PCM adjusts injector pulse width to supply a predetermined amount of additional fuel.

Ignition Switch In OFF Position

This is an open loop mode. All fuel injection is stopped and fuel flow is electrically shut down at both low-pressure and high-pressure fuel shutoff solenoids. PCM de-energizes auto shutdown relay and drives AIS motor into position in anticipation of next start-up.