Dodge Dakota (ND). Manual - part 227

MODULE-POWERTRAIN CONTROL

DESCRIPTION

The PCM (1) is attached to the right-inner corner of
the engine compartment.

DESCRIPTION - MODES OF OPERATION

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 program-
ming. Input from the oxygen (O2S) sensors is not monitored during Open Loop modes.

During Closed Loop modes, the PCM will monitor the oxygen (O2S) 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 O2S 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.

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ELECTRONIC CONTROL MODULES - SERVICE INFORMATION

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 (IAC) motor.

•

The PCM determines atmospheric air pressure from the MAP sensor input to determine basic fuel strategy.

•

The PCM monitors the engine coolant temperature sensor input. The PCM modifies fuel strategy based on this
input.

•

Intake manifold air temperature sensor input is monitored.

•

Throttle position sensor (TPS) is monitored.

•

The auto shutdown (ASD) 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 approx-
imately three seconds unless the engine is operating or the starter motor is engaged.

•

The O2S sensor heater element is energized via the ASD relay. The O2S 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 manifold air temperature sensor

•

Manifold absolute pressure (MAP) sensor

•

Throttle position sensor (TPS)

•

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.

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 manifold air temperature sensor

•

Manifold absolute pressure (MAP) sensor

•

Throttle position sensor (TPS)

•

Camshaft position sensor signal

•

Park/neutral switch (gear indicator signal—auto. trans. only)

•

Air conditioning select signal (if equipped)

•

Air conditioning request signal (if equipped)

Based on these inputs the following occurs:

•

The PCM adjusts engine idle speed through the idle air control (IAC) 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.

ELECTRONIC CONTROL MODULES - SERVICE INFORMATION

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•

When engine has reached operating temperature, the PCM will begin monitoring O2S sensor input. The sys-
tem 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 manifold air temperature sensor

•

Manifold absolute pressure (MAP) sensor

•

Throttle position sensor (TPS)

•

Camshaft position sensor signal

•

Battery voltage

•

Park/neutral switch (gear indicator signal—auto. trans. only)

•

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 O2S sensor input and adjusts air-fuel ratio by varying injector pulse width. It also
adjusts engine idle speed through the idle air control (IAC) 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

•

Engine coolant temperature sensor

•

Crankshaft position sensor

•

Intake manifold air temperature sensor

•

Manifold absolute pressure (MAP) sensor

•

Throttle position sensor (TPS)

•

Camshaft position sensor signal

•

Park/neutral switch (gear indicator signal—auto. trans. only)

•

Oxygen (O2S) 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 injector
pulse width by turning the ground circuit to each individual injector on and off.

•

The PCM monitors the O2S sensor input and adjusts air-fuel ratio. It also adjusts engine idle speed through
the idle air control (IAC) 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.

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ELECTRONIC CONTROL MODULES - SERVICE INFORMATION

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

•

Engine coolant temperature sensor

•

Crankshaft position sensor

•

Intake manifold air temperature sensor

•

Manifold absolute pressure (MAP) sensor

•

Throttle position sensor (TPS)

•

Camshaft position sensor signal

•

Park/neutral switch (gear indicator signal—auto. trans. only)

•

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 a 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 (IAC) 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 manifold air temperature sensor

•

Manifold absolute pressure (MAP) sensor

•

Throttle position sensor (TPS)

•

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.

OPERATION

The PCM is a pre-programmed, microprocessor digital computer. It regulates ignition timing, air-fuel ratio, emission
control devices, charging system, certain transmission features, speed control, air conditioning compressor clutch
engagement and idle speed. The PCM can adapt its programming to meet changing operating conditions.

ELECTRONIC CONTROL MODULES - SERVICE INFORMATION

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