Modes Of Operation

WARNING: This page is about a different car, the 2003 Dodge Dakota. However, it is still accessible from the selected car via links, so may be relevant.

As input signals to the Powertrain Control Module (PCM) change, the PCM adjusts its response to the output devices. The PCM will operate in two different modes: Open Loop and Closed Loop. During Open Loop modes, the PCM receives input signals and responds only according to preset PCM programming. Input from the Oxygen (O2) sensors is not monitored during Open Loop modes. During Closed Loop modes, the PCM will monitor the O2 sensors input. This input indicates to the PCM whether or not the calculated injector pulse width results in the ideal air-fuel ratio. This ratio is 14.7 parts air-to-1 part fuel. By monitoring the exhaust oxygen content through the O2 sensor, the PCM can fine tune the injector pulse width. This is done to achieve optimum fuel economy combined with low emission engine performance. The fuel injection system has the following modes of operation:

Ignition Switch ON
Engine Start-Up (Crank)
Engine Warm-Up
Idle
Cruise
Acceleration
Deceleration
Wide Open Throttle (WOT)
Ignition Switch OFF

The ignition switch On, engine start-up (crank), engine warm-up, acceleration, deceleration and wide open throttle modes are Open Loop modes. The idle and cruise modes, (with the engine at operating temperature) are Closed Loop modes.

IGNITION SWITCH (KEY-ON) MODE - This is an Open Loop mode. When the fuel system is activated by the ignition switch, the following actions occur:

The PCM pre-positions the idle air control motor.
The PCM determines atmospheric air pressure from the MAP sensor input toil determine basic fuel strategy.
The PCM monitors the engine coolant temperature sensor input. The PCM modifies fuel strategy based on this input.
Intake air temperature sensor input is monitored.
Throttle position sensor is monitored.
The auto shutdown relay is energized by the PCM for approximately three seconds.
The fuel pump is energized through the fuel pump relay by the PCM. The fuel pump will operate for approximately three seconds unless the engine is operating or the starter motor is engaged.
The O2 sensor heater element is energized via the ASD relay. The O2 sensor input is not used by the PCM to calibrate air-fuel ratio during this mode of operation.

ENGINE START-UP MODE - This is an Open Loop mode. The following actions occur when the starter motor is engaged. The PCM receives inputs from:

Battery Voltage
Engine Coolant Temperature Sensor
Crankshaft Position Sensor
Intake Air Temperature Sensor
Manifold Absolute Pressure Sensor
Throttle Position Sensor
Starter Motor Relay
Camshaft Position Sensor Signal

The PCM monitors the crankshaft position sensor. If the PCM does not receive A crankshaft position sensor signal within 3 seconds of cranking the engine, it will shut down the fuel injection-system. The fuel pump is activated by the PCM through the fuel pump relay. Voltage is applied to the fuel injectors with the ASD relay via the PCM. The PCM will then control the injection sequence and injector pulse width by turning the ground circuit to each individual injector on and off. The PCM determines the proper ignition timing according to input received from the crankshaft position sensor.

ENGINE WARM-UP MODE - This is an Open Loop mode. During engine warm-up the PCM receives inputs from:

Battery Voltage
Crankshaft Position Sensor
Engine Coolant Temperature Sensor
Intake Air Temperature Sensor
Manifold Absolute Pressure Sensor
Throttle Position Sensor
Camshaft Position Sensor Signal
Park/Neutral Switch (Gear Indicator Signal)
Air Conditioning Select Signal (If Equipped)
Air Conditioning Request Signal (If Equipped)

Based on these inputs the following occurs:

Voltage is applied to the fuel injectors with the ASD relay via the PCM. The PCM will then control the injection sequence and injector pulse width by turning the ground circuit to each individual injector on and off.
The PCM adjusts engine idle speed through the idle air control motor and adjusts ignition timing.
The PCM operates the A/C compressor clutch through the clutch relay. This is done if A/C has been selected by the vehicle operator and requested by the A/C thermostat.
When engine has reached operating temperature, the PCM will begin monitoring O2 sensor input. The system will then leave the warm-up mode and go into closed loop operation

IDLE MODE - When the engine is at operating temperature, this is a Closed Loop mode. At idle speed, the PCM receives inputs from:

Air Conditioning, Select Signal (If Equipped)
Air Conditioning, Request Signal (If Equipped)
Battery Voltage
Crankshaft Position Sensor
Engine Coolant Temperature Sensor
Intake Air Temperature Sensor
Manifold Absolute Pressure Sensor
Throttle Position Sensor
Camshaft Position Sensor Signal
Park/Neutral Switch (Gear Indicator Signal)
Oxygen Sensors

Based on these inputs, the following occurs:

Voltage is applied to the fuel injectors with the ASD relay via the PCM. The PCM will then control injection sequence and injector pulse width by turning the ground circuit to each individual injector on and off.
The PCM monitors the O2 sensor input and adjusts air-fuel ratio by varying injector pulse width. It also adjusts engine idle speed through the idle air control motor.
The PCM adjusts ignition timing by increasing and decreasing spark advance.
The PCM operates the A/C compressor clutch through the clutch relay. This happens if A/C has been selected by the vehicle operator and requested by the A/C thermostat.

CRUISE MODE - When the engine is at operating temperature, this is a Closed Loop mode. At cruising speed, the PCM receives inputs from:

Air Conditioning, Select Signal (If Equipped)
Air Conditioning, Request Signal (If Equipped)
Battery Voltage
Crankshaft Position Sensor
Engine Coolant Temperature Sensor
Intake Manifold Air Temperature Sensor
Manifold Absolute Pressure Sensor
Throttle Position Sensor
Camshaft Position Sensor Signal
Park/Neutral Switch (Gear Indicator Signal)
Oxygen Sensors

Based on these inputs, the following occurs:

Voltage is applied to the fuel injectors with the ASD relay via the PCM. The PCM will then adjust the injection pulse width to each individual injector on and off.
The PCM monitors the O2 sensor input and adjusts air-fuel ratio. It also adjusts engine idle speed through the idle air control motor.
The PCM adjusts ignition timing by turning the ground path to the coil on and off.
The PCM operates the A/C compressor clutch through the clutch relay. This happens if A/C has been selected by the vehicle operator and requested by the A/C thermostat.

ACCELERATION MODE - This is an Open Loop mode. The PCM recognizes an abrupt increase in throttle position or MAP pressure as a demand for increased engine output and vehicle acceleration. The PCM increases injector pulse width in response to increased throttle opening.

DECELERATION MODE - When the engine is at operating temperature, this is an Open Loop mode. During hard deceleration, the PCM receives the following inputs:

Air Conditioning, Select Signal (If Equipped)
Air Conditioning, Request Signal (If Equipped)
Battery Voltage
Crankshaft Position Sensor
Engine Coolant Temperature Sensor
Intake Air Temperature Sensor
Manifold Absolute Pressure Sensor
Throttle Position Sensor
Camshaft Position Sensor Signal
Park/Neutral Switch (Gear Indicator Signal)
Vehicle Speed Sensor

If the vehicle is under hard deceleration with the proper RPM and closed throttle conditions, the PCM will ignore the oxygen sensor input signal. The PCM will enter a fuel cut-off strategy in which it will not supply a ground to the injectors. If hard deceleration does not exist, the PCM will determine the proper injector pulse width and continue injection. Based on the above inputs the PCM will adjust engine idle speed through the idle air control motor. The PCM adjusts ignition timing by turning the ground path to the coil on and off.

WIDE OPEN THROTTLE MODE - This is an Open Loop mode. During wide open throttle operation, the PCM receives the following inputs:

Battery Voltage
Crankshaft Position Sensor
Engine Coolant Temperature Sensor
Intake Air Temperature Sensor
Manifold Absolute Pressure Sensor
Throttle Position Sensor
Camshaft Position Sensor Signal

During wide open throttle conditions, the following occurs:

Voltage is applied to the fuel injectors with the ASD relay via the PCM. The PCM will then control the injection sequence and injector pulse width by turning the ground circuit to each individual injector on and off. The PCM ignores the oxygen sensor input signal and provides a predetermined amount of additional fuel. This is done by adjusting injector pulse width.
The PCM adjusts ignition timing by turning the ground path to the coil on and off.

IGNITION SWITCH OFF MODE - When ignition switch is turned to OFF position, the PCM stops operating the injectors, ignition coil, ASD relay and fuel pump relay.