Chrysler Le Baron, Dodge Dynasty, Plymouth Acclaim. Instruction - page 50

VEHICLE SPEED AND DISTANCE INPUT—PCM
INPUT

On vehicles equipped with an electronic transaxle

(41TE), the transaxle output speed sensor supplies
the vehicle speed and distance inputs to the PCM.
The output speed sensor is located on the side of the
transaxle (Fig. 9).

The speed and distance signals, along with a closed

throttle signal from the TPS, determine if a closed
throttle deceleration or normal idle condition (vehicle
stopped) exists. Under deceleration conditions, the
PCM adjusts the idle air control motor to maintain a
desired MAP value. Under idle conditions, the PCM
adjusts the idle air control motor to maintain a de-
sired engine speed.

VEHICLE SPEED SENSOR—PCM INPUT

Vehicles with 3 speed automatic transaxles or

manual transaxles use vehicle speed sensors. On
both transaxles, the vehicle speed sensor (Fig. 11) is
located on the extension housing. The sensor input is
used by the PCM to determine vehicle speed and dis-
tance traveled.

The vehicle speed sensor generates 8 pulses per

sensor revolution. These signals, along with a closed
throttle signal from the TPS, determine if a closed
throttle deceleration or normal idle condition (vehicle
stopped) exists. Under deceleration conditions, the
PCM adjusts the idle air control motor to maintain a
desired MAP value. Under idle conditions, the PCM
adjusts the idle air control motor to maintain a de-
sired engine speed.

AIR CONDITIONING (A/C) CLUTCH RELAY (AC
BODY)—PCM OUTPUT

The PCM operates the air conditioning clutch relay

ground circuit. The ignition switch supplies battery
power to the solenoid side of the relay. The A/C fan
relay is operated independently of the PCM by the

Fan Cutout switch. When the A/C clutch relay ener-
gizes, battery voltage powers the A/C compressor
clutch.

With the engine operating and the blower motor

switch in the On position, the PCM turns the A/C
clutch on when the A/C switch closes. When the
PCM senses low idle speeds or wide open throttle
through the throttle position sensor, it de-energizes
the A/C clutch relay. The relay contacts open, pre-
venting air conditioning clutch engagement.

On AC body vehicles, the relay is located in the

power distribution center (Fig. 12).

AIR CONDITIONING (A/C) CLUTCH RELAY (AA, AG,
AJ BODY)—PCM OUTPUT

The PCM operates the air conditioning clutch relay

ground circuit. The ignition switch supplies battery
power to the solenoid side of the relay. When the A/C
clutch relay energizes, battery voltage powers the
A/C compressor clutch.

With the engine operating and the blower motor

switch in the On position, the PCM cycles the air
conditioning clutch on and off when the A/C switch
closes. When the PCM senses low idle speeds or wide
open throttle through the throttle position sensor, it
de-energizes the A/C clutch relay. The relay contacts
open, preventing air conditioning clutch engagement.

On AA body vehicles, the relay is located next to

the drivers side strut tower (Fig. 13).

On AG and AJ body vehicles, the relay is located

in the power distribution center (Fig. 14).

GENERATOR FIELD—PCM OUTPUT

The PCM regulates the charging system voltage

within a range of 12.9 to 15.0 volts. Refer to Group
8A for charging system information.

Fig. 11 Vehicle Speed Sensor—Typical

Fig. 12 Relay Identification (AC Body)

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AUTO SHUTDOWN (ASD) RELAY AND FUEL PUMP
RELAY—PCM OUTPUT

The PCM operates the auto shutdown (ASD) relay

and fuel pump relay through one ground path. The
PCM operates the relays by switching the ground
path on and off. Both relays turn on and off at the
same time.

The ASD relay connects battery voltage to the fuel

injector and ignition coil. The fuel pump relay con-
nects battery voltage to the fuel pump and oxygen
sensor heating element.

The PCM turns the ground path off when the igni-

tion switch is in the Off position. Both relays are off.
When the ignition switch is in the On or Crank po-
sition, the PCM monitors the distributor pick-up sig-
nal to determine engine speed and ignition timing

(coil dwell). If the PCM does not receive a distributor
signal when the ignition switch is in the Run posi-
tion, it will de-energize both relays. When the relays
are de-energized, battery voltage is not supplied to
the fuel injector, ignition coil, fuel pump and oxygen
sensor heating element.

On AA body vehicles, the relays are located next to

the drivers side strut tower (Fig. 13).

On AC, AG and AJ body vehicles, the relays are lo-

cated in the power distribution center (Fig. 12 or Fig.
14).

IDLE AIR CONTROL MOTOR—PCM OUTPUT

The idle air control motor is mounted on the throt-

tle body and is controlled by the PCM (Fig. 10). The
PCM adjusts engine idle speed through the idle air
control motor to compensate for engine load or ambi-
ent conditions.

The throttle body has an air bypass passage that

provides air for the engine at idle (the throttle blade
is closed). The idle air control motor pintle protrudes
into the air bypass passage and regulates air flow
through it.

The PCM adjusts engine idle speed by moving the

idle air control motor pintle in and out of the bypass
passage. The adjustments are based on inputs the
PCM receives. The inputs are from the throttle posi-
tion sensor, engine speed sensor (distributor pick-up
coil), coolant temperature sensor, and various switch
operations (brake, park/neutral, air conditioning).
Deceleration die out is also prevented by increasing
airflow when the throttle is closed quickly after a
driving (speed) condition.

DUTY CYCLE EVAP CANISTER PURGE
SOLENOID—PCM OUTPUT

The duty cycle EVAP purge solenoid regulates the

rate of vapor flow from the EVAP canister to the
throttle body. The powertrain control module oper-
ates the solenoid.

During the cold start warm-up period and the hot

start time delay, the PCM does not energize the so-
lenoid. When de-energized, no vapors are purged.
The PCM de-energizes the solenoid during open loop
operation.

The engine enters closed loop operation after it

reaches a specified temperature and the time delay
ends. During closed loop operation, the PCM ener-
gizes and de-energizes the solenoid approximately 5
to 10 times per second, depending upon operating
conditions. The PCM varies the vapor flow rate by
changing solenoid pulse width. Pulse width is the
amount of time the solenoid energizes.

A rubber boot covers the EVAP purge solenoid.

The solenoid and bracket attach to the EVAP canis-
ter mounting studs (Fig. 15). The top of the solenoid
has the word TOP on it. The solenoid will not oper-
ate unless it is installed correctly.

Fig. 13 Relay Identification (AA Body)

Fig. 14 Relay Identification (AG and AJ Body)

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MALFUNCTION INDICATOR LAMP (CHECK ENGINE
LAMP)—PCM OUTPUT

The malfunction indicator lamp (instrument panel

Check Engine lamp) comes on each time the ignition
key is turned ON and stays on for 3 seconds as a bulb
test. The malfunction indicator lamp warns the opera-
tor that the PCM has entered a Limp-in mode. During
Limp-in Mode, the PCM attempts to keep the system
operational. The malfunction indicator lamp signals
the need for immediate service. In limp-in mode, the
PCM compensates for the failure of certain components
that send incorrect signals. The PCM substitutes for
the incorrect signals with inputs from other sensors.

Signals that can trigger the malfunction indi-

cator lamp (Check Engine Lamp).
• Engine Coolant Temperature Sensor

• Manifold Absolute Pressure Sensor

• Throttle Position Sensor

• Battery Voltage Input

• An Emission Related System (California vehicles)

• Charging system

The malfunction indicator lamp displays diagnostic

trouble codes. Cycle the ignition switch on, off, on, off,
on, within five seconds to display any diagnostic
trouble codes stored in the PCM. Refer to the 3.0L
Multi-Port Fuel Injection—On-Board Diagnostics sec-
tion of this Group for Diagnostic trouble code Descrip-
tions.

DATA LINK CONNECTOR—PCM OUTPUT

The data link connector provides the technician with

the means to connect the DRBII scan tool to diagnosis
the vehicle.

TRANSAXLE CONTROL MODULE—PCM OUTPUT

The PCM supplies the following information to the

electronic automatic transaxle control module through
the CCD Bus:
• battery temperature

• brake switch input

• engine coolant temperature

• manifold absolute pressure (MAP)

• speed control information

FUEL INJECTORS—PCM OUTPUT

The fuel injectors are electrical solenoids (Fig. 16).

The injector contains a pintle that closes off an ori-
fice at the nozzle end. When electric current is sup-
plied to the injector, the armature and pintle move a
short distance against a spring, allowing fuel to flow
out the orifice. Because the fuel is under high pres-
sure, a fine spray is developed in the shape of a hol-
low cone. The spraying action atomizes the fuel,
adding it to the air entering the combustion cham-
ber.

The injectors are positioned in the intake manifold

with the nozzle ends directly above the intake valve
port (Fig. 16).

The fuel injectors are operated by the PCM. They

are energized in a sequential order during all engine
operating conditions except start up. The PCM ini-

Fig. 16 Fuel Injector—3.0L Engine

Fig. 17 Fuel Injector Location

Fig. 15 EVAP Purge Solenoid

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FUEL SYSTEMS

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tially energizes all injectors at the same time. Once
the PCM determines crankshaft position, it begins
energizing the injectors in sequence.

Battery voltage is supplied to the injectors through

the ASD relay. The PCM provides the ground path
for the injectors. By switching the ground path on
and off, the PCM adjusts injector pulse width. Pulse
width is the amount of time the injector is energized.
The PCM adjusts injector pulse width based on in-
puts it receives.

IGNITION COIL—PCM OUTPUT

The auto shutdown (ASD) relay provides battery

voltage to the ignition coil. The PCM provides a
ground contact (circuit) for energizing coil. When the
PCM breaks the contact, the energy in the coil pri-
mary transfers to the secondary causing the spark.
The PCM will de-energize the ASD relay if it does
not receive an input from the distributor pick-up. Re-
fer to Auto Shutdown (ASD) Relay/Fuel Pump Re-
lay—PCM Output in this section for relay operation.

The ignition coil is mounted on a bracket next to

the air cleaner (Fig. 18).

PART THROTTLE UNLOCK SOLENOID—PCM
OUTPUT

Three-speed automatic transaxles use a part throt-

tle unlock solenoid. The PCM controls the lock-up of
the torque convertor through the part throttle unlock
solenoid. The transaxle is locked up only in direct
drive mode. Refer to Group 21 for transaxle informa-
tion.

RADIATOR FAN RELAY—PCM OUTPUT

The radiator fan is energized by the PCM through

the radiator fan relay. The radiator fan relay is lo-
cated on the drivers side fender well near to the
PCM. The PCM grounds the relay when engine cool-
ant reaches a predetermined temperature or the air
conditioning system turns on.

On AA body vehicles, the relay is located next to

the drivers side strut tower (Fig. 13).

On AC, AG and AJ body vehicles, the relay is lo-

cated in the power distribution center (Fig. 12 or Fig.
14).

SPEED CONTROL SOLENOIDS—PCM OUTPUT

The speed control vacuum and vent solenoids are

operated by the PCM. When the PCM supplies a
ground to the vacuum and vent solenoids, the speed
control system opens the throttle blade. When the
PCM supplies a ground only to the vent solenoid, the
throttle blade holds position. When the PCM removes
the ground from both the vacuum and vent solenoids,
the throttle blade closes. The PCM balances the two
solenoids to maintain the set speed. Refer to Group
8H for speed control information.

TACHOMETER—PCM OUTPUT

The PCM supplies engine RPM to the instrument

panel tachometer through the CCD Bus. The CCD
Bus is a communications port. Various modules use
the CCD Bus to exchange information. Refer to
Group 8E for more information.

MODES OF OPERATION

As input signals to the PCM change, the PCM ad-

justs its response to the output devices. For example,
the PCM must calculate a different injector pulse
width and ignition timing for idle than for wide open
throttle (WOT). There are several different modes of
operation that determine how the PCM responds to
the various input signals.

There are two different areas of operation, OPEN

LOOP and CLOSED LOOP.

During OPEN LOOP modes the PCM receives in-

put signals and responds according to preset PCM
programming. Input from the oxygen (O

2

) sensor is

not monitored during OPEN LOOP modes.

During CLOSED LOOP modes the PCM does mon-

itor the oxygen (O

2

) sensor input. This input indi-

cates to the PCM if the injector pulse width results
in an air-fuel ratio of 14.7 parts air to 1 part fuel. By
monitoring the exhaust oxygen content through the
O

2

sensor, the PCM can fine tune the injector pulse

width. Fine tuning injector pulse width allows the
PCM to achieve optimum fuel economy combined
with low emissions.

The 3.0L sequential MPI system 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

Fig. 18 Ignition Coil

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