1993 DODGE TRUCK sensor

•

FUEL
SYSTEM
14-29
MULTI-PORT
FUEL
INJECTION
(MPI)-COMPONENT DESCRIPTION/SYSTEM
OPERATION-EXCEPT DIESEL

INDEX

page

Air
Conditioning (A/C) Clutch
Relay-Pern
Output
. 35

Air
Conditioning (A/C)
Controls—PCM
Input
.... 31

Auto
Shut
Down
(ASD)
Relay-PCM
Output
. ... 36

Automatic
Shut
Down
(ASD)
Sense-PCM
Input
. 31
Battery
Voltage-PCM
Input
32

Brake
Switch-PCM
Input
32

Camshaft
Position
Sensor—PCM
Input
32

Charge
Air
Temperature
Sensor—PCM
Input
. . . 32

Crankshaft
Position
Sensor-PCM
Input
.......
32
Electric
Exhaust
Gas Recirculation Transducer
(EET)
Solenoid-PCM
Output
...
.......
36

Engine
Coolant Temperature
Sensor—PCM
Input
. 33

EVAP
Canister
Purge
Solenoid—PCM
Output
. . . 37

Fuel
Injectors-PCM Output
37
Fuel
Pressure
Regulator
41

Fuel
Rail
41

General
Information
.......................
29

Generator
Field-PCM
Output
36

Generator
Lamp-PCM
Output
36
Idle
Air
Control
(IAC)
Motor-PCM
Output
......
36

Ignition
Circuit
Sense—PCM
Input
33

GENERAL
INFORMATION
All
gas
powered engines
are
equipped with sequen­
tial Multi-Port Fuel Injection (MPI).
The MPI
system (Fig.
1)
provides precise air/fuel ratios
for all
driving
conditions. The Powertrain Control Module
(PCM)
operates
the fuel system.
The PCM was
formerly referred
to
as
the
SBEC
or
engine controller.
The PCM is a
pre­
programmed, dual microprocessor digital computer. It regulates ignition timing, air-fuel ratio, emission
control devices, charging system, speed control,
air
conditioning compressor clutch engagement
and
idle speed.
The PCM can
adapt
its
programming
to
meet
changing operating conditions.
Powertrain Control Module (PCM) Inputs rep­
resent
the
instantaneous engine operating conditions.
Air-fuel mixture
and
ignition timing calibrations
for

various driving
and
atmospheric conditions
are
pre­
programmed into
the PCM. The PCM
monitors
and
analyzes various inputs.
It
then computes engine fuel
and ignition timing requirements based
on
these
in­

puts.
Fuel delivery control
and
ignition timing will
then
be
adjusted accordingly. Other inputs
to the
PCM
are
provided
by the
brake
light switch,
air
conditioning select switch
and the

speed control switches.
All
inputs
to the PCM are

converted into signals. Electrically operated fuel injectors spray fuel
in

precise metered amounts into
the
intake port directly above
the
intake valve.
The
injectors
are
fired
in a

specific sequence
by the PCM. The PCM
maintains
page

Ignition
Coil-PCM
Output
37

Malfunction Indicator
Lamp—PCM
Output
37

Manifold
Absolute
Pressure
(MAP)
Sensor-
PCM
Input
33

Open
Loop/Closed
Loop
Modes
of
Operation
. . . 38

Overdrive/Override
Switch
34

Oxygen
(02)
Sensor—PCM
Input
33

Park/Neutral
Switch—PCM
Input
34

Power
Ground
34

Powertrain Control Module
(PCM)
30

SCI
Receive-PCM
Input
. 34

SCI
Transmit-PCM
Output
37

Sensor
Return
—PCM
Input
35

Shift Indicator-PCM Output
38

Speed
Control-PCM
Input
34
Speed
Control-PCM
Output
38

SRI
Lamp-PCM
Output
36

Tachometer—PCM
Output
38

Throttle
Body
40

Throttle
Position
Sensor
(TPS)-PCM
Input
35

Vehicle
Speed
Sensor-PCM
Input
35

an air/fuel ratio
of 14.7 to 1 by
constantly adjusting
injector pulse width. Injector pulse width
is the

length
of
time that
the
injector opens
and
sprays fuel into
the
chamber.
The PCM
adjusts injector pulse
width
by
opening
and
closing
the
ground path
to the
injector.
Manifold absolute pressure
(air
density)
and
engine
rpm (speed)
are the
primary inputs that determine
fuel injector pulse width.
The PCM
also monitors
other inputs when adjusting air-fuel ratio.
Inputs That Effect Fuel Injector Pulse Width:
• Exhaust
gas
oxygen content
• Coolant temperature
• Manifold absolute pressure (MAP)
• Engine speed
• Throttle position
• Battery voltage •
Air
conditioning selection
• Transmission gear selection (auto, trans.)
• Speed control The powertrain control module (PCM) adjusts igni­
tion timing
by
controlling ignition coil operation.
The

ignition coil receives battery voltage when
the
igni­
tion
key is in the run or
starter (crank) position.
The

PCM provides
a
ground
for the
ignition coil.
The
coil
discharges when
the PCM
supplies
a
ground.
By
switching
the
ground path
on and off, the PCM
reg­
ulates ignition timing.
The sensors
and
switches that provide inputs
to the

powertrain control module
(PCM)
comprise
the En-

14
- 30
FUEL
SYSTEM

INPUTS

OUTPUTS
POWERTRAIN
CONTROL
MODULE
DRB
II

SCAN
TOOL

SPEED

CONTROL

BRAKE

SWITCH
A/C
LOW

PRESSURE
CUTOFF
SWITCH VEHICLE

SPEED
SENSOR PARK/NEUTRAL
SWITCH TORQUE CONVERTER
CLUTCH SOLENOID
MALFUNCTION

INDICATOR
LAMP
m
HEATED
i

*OXYGEN SENSOR ENGINE
COOLANT
yy
BATTERY
TEMPERATURE

SENSOR
MAP SENSOR

i—r
CHARGE
AIR
TEMPERATURE
SENSOR
AIR CHARGE
TEMPERATURE
SENSOR
DISTRIBUTOR

WITH
CAMSHAFT
r
POSITION
SENSOR
(|
TACHOMETER

A/C
CLUTCH RELAY
AUTO
SHUTDOWN
RELAY OVERDRIVE
SOLENOID
IDLE AIR
CONTROL MOTOR
SPEED

CONTROL
SHIFT

INDICATOR

LAMP

EMISSION

CONTROL SOLENOIDS
IGNITION
COIL
OVERDRIVE
OVERRIDE SWITCH
ASD

SENSE
FUEL
INJECTORS
PARK
THROTTLE

SOLENOID
GENERATOR CRANKSHAFT
POSITION FUEL
PUMP
RELAY
J9314-117

Fig.
1 Multi-Port
Fuel
Injection
Components—Except
Diesel

gine Control System. It is also comprised of the PCM Outputs (engine control devices that the are operated
by the PCM).

SYSTEM DIAGNOSIS
The powertrain control module (PCM) tests many
of its own input and output circuits. If a diagnostic
trouble code (DTC) is found in a major system, this information is stored in the PCM memory. Refer to
On-Board Diagnostics in the Multi-Port Fuel Injec­
tion—General Diagnosis—Except Diesel section of
this group for DTC information.

POWERTRAIN
CONTROL MODULE (PCM)
The Powertrain Control Module (PCM) (Fig. 2) op­
erates the fuel system. The PCM was formerly re­
ferred to as the SBEC or engine controller. The PCM is a pre-programmed, dual microprocessor digital computer. It regulates ignition timing, air-fuel ratio, emission control devices, charging system, speed con­trol, air conditioning compressor clutch engagement
A/C
CLUTCH RELAY STARTER RELAY
TORQUE CONVERTER CLUTCH RELAY
AUTO
SHUTDOWN RELAY
FUEL PUMP RELAY
DATA UNK
CONNECTOR
POWERTRAIN

CONTROL MODULE
J9314-164

Fig.
2 Powertrain Control
Module
(PCM) Location and idle speed. The PCM can adapt its programming
to meet changing operating conditions.
The PCM receives input signals from various
switches and sensors. Based on these inputs, the
PCM regulates various engine and vehicle operations

•

FUEL SYSTEM
14-31 through different system components. These compo­
nents are referred to as Powertrain Control Module
(PCM) Outputs. The sensors and switches that pro­
vide inputs to the PCM are considered Powertrain Control Module (PCM) Inputs.
The PCM adjusts ignition timing based upon in­
puts it receives from sensors that react to: engine rpm, manifold absolute pressure, engine coolant tem­
perature, throttle position, transmission gear selec­
tion (automatic transmission), vehicle speed and the
brake switch.
The PCM adjusts idle speed based on inputs it re­
ceives from sensors that react to: throttle position,
vehicle speed, transmission gear selection, engine coolant temperature and from inputs it receives from
the air conditioning clutch switch and brake switch.
Based on inputs that it receives, the PCM adjusts
ignition coil dwell. The PCM also adjusts the gener­
ator charge rate through control of the generator
field and provides speed control operation.
Powertrain Control Module (PCM) Inputs:
• Generator output • A/C request (if equipped with factory A/C)
• A/C select (if equipped with factory A/C)
• Auto shut down (ASD) sense
• Charge air temperature sensor
• Battery voltage
• Brake switch
• Engine coolant temperature sensor
• Crankshaft position sensor • Ignition circuit sense (ignition switch in run posi­
tion)
• Manifold absolute pressure (MAP) sensor
• Overdrive/override switch
• Oxygen sensor(s)
• Park/neutral switch (auto, trans, only)
• SCI receive (DRB II connection) • Speed control resume switch
• Speed control set switch • Speed control on/off switch
• Camshaft position sensor signal
• Throttle position sensor
• Vehicle speed sensor
• Sensor return
• Power ground
• Signal ground Powertrain Control Module (PCM) Outputs:
• A/C clutch relay
• Idle air control (IAC) motor
• Auto shut down (ASD) relay
• Generator field
• Malfunction indicator lamp
• Service reminder indicator lamp
• EGR valve control solenoid • Fuel injectors
• Fuel pump relay
• Ignition coil • EVAP canister purge solenoid
• SCI transmit (DRB II connection)
• Shift indicator lamp (manual transmission only)
• Speed control vacuum solenoid
• Speed control vent solenoid
• Tachometer (on instrument panel, if equipped) The powertrain control module (PCM) contains a
voltage convertor. This converts battery voltage to a
regulated 8.0 volts. It is used to power the crankshaft
position sensor and camshaft position sensor. The
PCM also provides a five (5) volt supply for the man­ ifold absolute pressure (MAP) sensor and throttle po­
sition sensor (TPS).

AIR
CONDITIONING
(A/C)
CONTROLS-PCM
INPUT
The A/C control system information applies to fac­
tory installed air conditioning units. A/C SELECT SIGNAL: When the A/C switch is
in the ON position and the A/C low pressure switch
is closed, an input signal is sent to the powertrain
control module (PCM). The signal informs the PCM
that the A/C has been selected. The PCM adjusts idle speed to a pre-programmed rpm through the idle air
control (IAC) motor to compensate for increased en­
gine load. A/C REQUEST SIGNAL: Once A/C has been se­
lected, the powertrain control module (PCM) receives
the A/C request signal from the evaporator switch.
The input indicates that the evaporator temperature is in the proper range for A/C application. The PCM
uses this input to cycle the A/C compressor clutch (through the A/C relay). It will also determine the
correct engine idle speed through the idle air control (IAC) motor position. If the A/C low pressure switch opens (indicating a
low refrigerant level), the PCM will not receive an
A/C select signal. The PCM will then remove the ground from the A/C relay. This will deactivate the
A/C compressor clutch. If the evaporator switch opens, (indicating that
evaporator is not in proper temperature range), the
PCM will not receive the A/C request signal. The
PCM will then remove the ground from the A/C re­ lay, deactivating the A/C compressor clutch.

AUTOMATIC SHUT DOWN
(ASD)
SENSE-PCM INPUT
A 12 volt signal at this input indicates to the PCM
that the ASD has been activated. The ASD relay is located in the engine compartment (Fig. 2). It is used
to connect the oxygen sensor(s) heater element, igni­
tion coil, generator field winding and fuel injectors to 12 volt + power supply. This input is used only to sense that the ASD relay
is energized. If the powertrain control module (PCM)
does not see 12 volts at this input when the ASD
should be activated, it will set a diagnostic trouble
code (DTC).

14
- 32
FUEL SYSTEM

•
BATTERY VOLTAGE—PCM
INPUT

The battery voltage input provides power
to the

powertrain control module (PCM).
It
also informs
the

PCM what voltage level
is
supplied
to the
ignition
coil
and
fuel injectors. If battery voltage
is low, the PCM
will increase injec­
tor pulse width (period
of
time that
the
injector
is
ener­
gized).
This
is
done
to
compensate
for the
reduced flow
through injector caused
by the
lowered voltage.

BRAKE
SWITCH-PCM
INPUT
When
the
brake light switch
is
activated,
the
pow­
ertrain control module
(PCM)
receives
an
input indi­
cating that
the
brakes
are
being applied. After
receiving this input,
the PCM
maintains idle speed
to
a
scheduled
rpm
through control
of the
idle
air
control
(IAC)
motor.
The
brake switch input
is
also
used
to
operate
the
speed control system.

CAMSHAFT POSITION SENSOR—PCM
INPUT
A sync signal
is
provide
by the
camshaft position sen­
sor located
in the
ignition distributor
(Fig.
3).
The
sync
signal from this sensor works
in
conjunction with
the

crankshaft position sensor
to
provide
the
powertrain
control module
(PCM)
with inputs. This
is
done
to es­

tablish
and
maintain correct injector firing order. Refer
to
Camshaft Position Sensor
in
Group
8D, Ig­

nition System
for
more information.

Fig.
3
Camshaft Position
Sensor

CHARGE AIR TEMPERATURE SENSOR-PCM
INPUT
The intake manifold charge
air
temperature sensor
is installed
in the
intake manifold with
the
sensor
el­

ement extending into
the air
stream
(Fig. 4). The
sensor provides
an
input voltage
to the
powertrain control module
(PCM)
indicating intake manifold
air

temperature.
The
input
is
used along with inputs from other sensors
to
determine injector pulse width. As
the
temperature
of the
air-fuel stream
in the
manifold varies,
the
sensor resistance changes. This
results
in a
different input voltage
to the PCM.

Fig.
4
Charge
Air
Temperature
Sensor—Typical

CRANKSHAFT POSITION SENSOR-PCM INPUT
This sensor
is a
hall effect device that detects
notches
in the
flywheel (manual transmission),
or
flexplate (automatic transmission). This sensor
is
used
to
indicate
to the
powertrain
control module
(PCM)
that
a
spark
and or
fuel injec­
tion event
is to be
required.
The
output from this sensor,
in
conjunction with
the
camshaft position
sensor signal,
is
used
to
differentiate between fuel
in­

jection
and
spark events.
It is
also used
to
synchro­ nize
the
fuel injectors with their respective cylinders. The sensor
is
bolted
to the
cylinder block near
the

rear
of the
right cylinder head
(Fig. 5).
Fig.
5
Crankshaft Position Sensor—Typical

•

FUEL SYSTEM
14 - 33 Refer to Group 8D, Ignition System for more crank­
shaft position sensor information. The engine will not operate if the PCM does not re­
ceive a crankshaft position sensor input.

ENGINE
COOLANT TEMPERATURE SENSOR-PCM
INPUT
The engine coolant temperature sensor is installed
next to the thermostat housing (Fig. 6) and protrudes
into the water jacket. The sensor provides an input
voltage to the powertrain control module (PCM) re­
lating coolant temperature. The PCM uses this input
along with inputs from other sensors to determine in­
jector pulse width and ignition timing. As coolant temperature varies, the coolant temperature sensor
resistance will change. This change in resistance re­sults in a different input voltage to the PCM. When the engine is cold, the PCM will operate in
Open Loop cycle. It will demand slightly richer air-
fuel mixtures and higher idle speeds. This is done until normal operating temperatures are reached.

Fig.
6 Coolant
Temperature
Sensor—
Typical

IGNITION CIRCUIT
SENSE-PCM
INPUT
The ignition circuit sense input tells the power-
train control module (PCM) the ignition switch has
energized the ignition circuit. Refer to the wiring di­
agrams for circuit information.

MANIFOLD ABSOLUTE
PRESSURE
(MAP)

SENSOR-PCM
INPUT
The MAP sensor reacts to absolute pressure in the
intake manifold. It provides an input voltage to the
powertrain control module (PCM). As engine load changes, manifold pressure varies. The change in
manifold pressure causes MAP sensor voltage to
change. The change in MAP sensor voltage results in a different input voltage to the PCM. The input volt­
age level supplies the PCM with information about
ambient barometric pressure during engine start-up (cranking) and engine load while the engine is run­ ning. The PCM uses this input along with inputs
from other sensors to adjust air-fuel mixture.
The MAP sensor is mounted on the side of the en­
gine throttle body (Fig. 7). The sensor is connected to
the throttle body with a rubber L-shaped fitting.

MANIFOLD
ABSOLUTE
Fig.
7 Manifold
Absolute
Pressure
(MAP)
Sensor—
Typical

OXYGEN
(02)
SENSOR—PCM
INPUT
3.9L/5.2L/S»9L
LDC
ENGINE
The single 02 sensor on the 3.9L, 5.2L or 5.9L light
duty cycle (LDC) engine is located in the exhaust
down pipe (Fig. 8). It provides an input voltage to the
powertrain control module (PCM) relating the oxy­
gen content of the exhaust gas. The PCM uses this
information to fine tune the air-fuel ratio by adjust­ ing injector pulse width.
The 02 sensor produces voltages from 0 to 1 volt.
This voltage will depend upon the oxygen content of
the exhaust gas in the exhaust manifold. When a large amount of oxygen is present (caused by a lean
air-fuel mixture), the sensor produces a low voltage.
When there is a lesser amount present (rich air-fuel
mixture) it produces a higher voltage. By monitoring
the oxygen content and converting it to electrical
voltage, the sensor acts as a rich-lean switch.
The oxygen sensor is equipped with a heating ele­
ment that keeps the sensor at proper operating tem­
perature during all operating modes. Maintaining
correct sensor temperature at all times allows the system to enter into closed loop operation sooner. In Closed Loop operation, the powertrain control
module (PCM) monitors the 02 sensor input (along
with other inputs). It then adjusts the injector pulse

14
- 34
FUEL SYSTEM

width accordingly. During Open Loop operation, the
PCM ignores the 02 sensor input and adjusts injector
pulse width to a preprogrammed value (based on other sensor inputs).

EXHAUST
PIPE J9214-5
Fig. 8 Oxygen Sensor Location—3.9L/5.2L/5.9L LDC Engine
5,9L HDC
ENGINE
Dual 02 sensors are used on the 5.9L heavy duty
cycle (HDC) engine (Fig. 9). Each sensor will monitor
the oxygen content in each exhaust downpipe. The left sensor monitors the odd numbered cylinders (1-3-5-7). The right sensor monitors the even numbered
cylinders (2-4-6-8),
For sensor operational information, refer to the
paragraphs in the previous 3.9L/5.2/5.9L LDC oxygen sensor section. Fig. 9 Oxygen Sensor Location—5.9L HDC Engine

OVERDRIVE/OWERRIDE
SWITCH
On vehicles equipped with overdrive, the power-
train control module (PCM) regulates the 3-4 over­ drive up-shift and down-shift through the overdrive solenoid. An override switch is located on the instru­
ment panel. The overdrive/override switch is normally closed. It
opens when the operator presses the switch. The
transmission will not enter overdrive when the oper­ ator presses the override switch. The transmission
downshifts if the operator presses the override switch
while in overdrive.
The overdrive switch circuit contains two other
switches: A transmission thermo-switch and a cool­
ant temperature switch. When either switch opens,
the transmission will not shift into overdrive, or downshift (if already in overdrive).
Refer to Group 21 for more information.

PARK/NEUTRAL SWITCH-PCM
INPUT
The park/neutral switch is located on the transmis­
sion housing and provides an input to the powertrain
control module (PCM). This will indicate that the au­
tomatic transmission is in Park, Neutral or a drive
gear selection. This input is used to determine idle
speed (varying with gear selection), fuel injector
pulse width and ignition timing advance. Refer to Group 21, Transmissions, for testing, replacement
and adjustment information.

POWER
GROUND
The power ground is used to control ground circuits
for the following powertrain control module (PCM)
loads:

• Generator field winding
• 8 volt (PCM) power supply
• Fuel injectors
• Ignition coil

SCI
RECEIVE-PCM
INPUT
SCI Receive is the serial data communication re­
ceive circuit for the DRB II scan tool. The powertrain
control module (PCM) receives data from the DRB II
through the SCI Receive circuit.

SPEED
CONTROL-PCM INPUT
The speed control system provides three separate
inputs to the powertrain control module (PCM); On/ Off, Set and Resume. The On/Off input informs the
PCM that the speed control system has been acti­
vated. The Set input informs the PCM that a fixed
vehicle speed has been selected. The Resume input indicates to the PCM that the previous fixed speed is
requested. The speed control operating range is from 50 km/h
to 142 km/h (35 to 85 mph). Inputs that effect speed control operation are:
• Park/neutral switch
• Vehicle speed sensor
• Throttle position sensor Refer to Group 8H for further speed control infor­
mation.

•

FUEL SYSTEM
14 - 35
SENSOR
RETURN—PCM
INPUT

Sensor Return provides a low noise ground refer­
ence for all system sensors.

THROTTLE POSITION
SENSOR
(TPS)-PCM
INPUT
The throttle position sensor (TPS) is mounted on
the throttle body (Fig. 10). The TPS is a variable re­ sistor that provides the powertrain control module (PCM) with an input signal (voltage) that represents
throttle blade position. The sensor is connected to the
throttle blade shaft. As the position of the throttle
blade changes, the resistance of the TPS changes. The PCM supplies approximately 5 volts to the

TPS.
The TPS output voltage (input signal to the PCM) represents the throttle blade position. The
PCM receives an input signal voltage from the TPS.
This will vary in an approximate range of from 1
volt at minimum throttle opening (idle), to 4 volts at
wide open throttle. Along with inputs from other sen­
sors,
the PCM uses the TPS input to determine cur­
rent engine operating conditions. In response to
engine operating conditions, the PCM will adjust fuel
injector pulse width and ignition timing.
MANIFOLD ABSOLUTE
Fig.
10
Throttle
Position Sensor—Typical

VEHICLE
SPEED
SENSOR—PCM
INPUT
The speed sensor (Fig. 11) is located in the exten­
sion housing of the transmission (2WD) or on the
transfer case extension housing (4WD). The sensor input is used by the powertrain control module (PCM) to determine vehicle speed and distance trav­
eled. The speed sensor generates 8 pulses per sensor rev­
olution. These signals, in conjunction with a closed
throttle signal from the throttle position sensor, indi­
cate a closed throttle deceleration to the PCM. When the vehicle is stopped at idle, a closed throttle signal
is received by the PCM (but a speed sensor signal is
not received).
Under deceleration conditions, the PCM adjusts the
idle air control (IAC) motor to maintain a desired
MAP value. Under idle conditions, the PCM adjusts
the IAC motor to maintain a desired engine speed.
Fig.
11 Vehicle
Speed
Sensor—Typical

AIR
CONDITIONING
(A/C)
CLUTCH RELAY—PCM
OUTPUT
The powertrain control module (PCM) activates the
A/C compressor through the A/C clutch relay. The
PCM regulates A/C compressor operation by switch­
ing the ground circuit for the A/C clutch relay on and off. The relay is located in the engine compart­
ment (Fig. 12).

A/C
CLUTCH RELAY STARTER RELAY
DATA LINK CONTROL
CONNECTOR MODULE
J9314-164

Fig.
12 Relay Location
When the PCM receives a request for A/C from A/C
evaporator switch, it will adjust idle air control (IAC)
motor position. This is done to increase idle speed.
The PCM will then activate the A/C clutch through
the A/C clutch relay. The PCM adjusts idle air con-

trol (IAC) stepper motor position to compensate for
increased engine load from the A/C compressor.
By switching the ground path for the relay on and
off, the PCM is able to cycle the A/C compressor
clutch. This is based on changes in engine operating
conditions. If, during A/C operation, the PCM senses
low idle speeds or a wide open throttle condition, it
will de-energize the relay. This prevents A/C clutch engagement. The relay will remain de-energized un­
til the idle speed increases or the wide open throttle condition exceeds 15 seconds or no longer exists. The
PCM will also de-energize the relay if coolant tem­
perature exceeds 125°C (257°F).

IDLE
AIR
CONTROL
(IAC)
MOTOR-PCM OUTPUT
The IAC motor is mounted to the back of the throt­
tle body (Fig. 13) and is controlled by the powertrain control module (PCM).
AAANIFOLD ABSOLUTE

PRESSURE
SENSOR
MOUNTING
SCREWS
MAP SENSOR

THROTTLE

POSITION
SENSOR
J9314-86

Fig.
13 IAC Motor—Typical The throttle body has an air control passage that
provides air for the engine at idle (the throttle plate is closed). The IAC motor pintle protrudes into the
air control passage (Fig. 14) and regulates air flow
through it. Based on various sensor inputs, the pow­
ertrain control module (PCM) adjusts engine idle speed by moving the IAC motor pintle in and out of
the air control passage. The IAC motor is positioned
when the ignition key is turned to the On position.
A (factory adjusted) set screw is used to mechani­
cally limit the position of the throttle body throttle
plate. Never attempt to adjust the engine idle speed using this screw. All idle speed functions are
controlled by the PCM.
RUBBER
FITTING

J9314-87

Fig.
14
Throttle
Body
Air Control
Passage

AUTO SHUT DOWN (ASD) RELAY—PCM OUTPUT
The ASD relay is located in the engine compart­
ment (Fig. 12). The ASD supplies battery voltage to the fuel pump,
fuel injector, ignition coil, generator field winding and oxygen (02) sensor(s) heating element. The
ground circuit for the coil in the ASD relay is con­
trolled by the powertrain control module (PCM). The PCM operates the relay by switching the ground cir­
cuit on and off. The fuel pump relay is controlled by the PCM
through same circuit that the ASD relay is con­ trolled.
GENERATOR FIELD-PCM OUTPUT

The powertrain control module (PCM) regulates
the charging system voltage within a range of 12.9 to 15.0 volts. Refer to Group 8A for charging system in­
formation.

GENERATOR LAMP-PCM OUTPUT
If the powertrain control module (PCM) senses a
low charging condition in the charging system, it
will illuminate the generator lamp on the instrument
panel. For example, during low idle with all accesso­
ries turned on, the light may momentarily go on. Once the PCM corrects idle speed to a higher rpm,
the light will go out. Refer to Group 8A for charging system information.

ELECTRIC
EXHAUST GAS RECIRCULATION

TRANSDUCER
(EET)
S0LEN0ID-PCM OUTPUT

Refer to Group 25, Emission Control System for in­
formation. See Electric Exhaust Gas Recirculation
Transducer (EET) Solenoid.

SRI
LAMP-PCM OUTPUT
The instrument panel mounted service reminder
indicator (SRI) lamp was formerly referred to as the
emission maintenance reminder (EMR) lamp. It is