turn signal DODGE RAM 2002 Service Repair Manual

OPERATION
Battery voltage is supplied to the CAB when a
speed of 15 miles per hour is reached. The CAB per-
forms a system initialization procedure at this point.
Initialization consists of a static and dynamic self
check of system electrical components.
The static and dynamic checks occurs at ignition
start up. During the dynamic check, the CAB briefly
cycles the pump and solenoids to verify operation. An
audible noise may be heard during this self check.
This noise should be considered normal.
If an ABS component exhibits a fault during ini-
tialization, the CAB illuminates the amber warning
light and registers a fault code in the microprocessor
memory.
The CAB monitors wheel speed sensor inputs con-
tinuously while the vehicle is in motion. However,
the CAB will not activate any ABS components as
long as sensor inputs indicate normal braking.
During normal braking, the master cylinder, power
booster and wheel brake units all function as they
would in a vehicle without ABS. The HCU compo-
nents are not activated.
The purpose of the antilock system is to prevent
wheel lockup during periods of high wheel slip. Pre-
venting lockup helps maintain vehicle braking action
and steering control.
The antilock CAB activates the system whenever
sensor signals indicate periods of wheel slip. Periods
of wheel slip occur when brake stops involve high
pedal pressure and rate of vehicle deceleration.
The antilock system prevents lockup during a
wheel slip condition by modulating fluid apply pres-
sure to the wheel brake units.
Brake fluid apply pressure is modulated according
to wheel speed, degree of slip and rate of decelera-
tion. Sensors at each front wheel convert wheel speed
into electrical signals. These signals are transmitted
to the CAB for processing and determination of
wheel slip and deceleration rate.
The ABS system has three fluid pressure control
channels. The front brakes are controlled separately
and the rear brakes in tandem. A speed sensor input
signal indicating a wheel slip condition activates the
CAB antilock program.
There are Two solenoid valves (Isolation and Dump
valve) which are used in each antilock control chan-
nel. The valves are all located within the HCU valve
body and work in pairs to either increase, hold, or
decrease apply pressure as needed in the individual
control channels.
During an ABS stop the ISO valve actuates, Stop-
ping anymore pressure build Ðup to the calipers.
Then the Dump valve dumps off pressure until the
wheel unlocks. This will continue until the wheels
quit slipping altogether.
DIAGNOSIS AND TESTING - ANTILOCK
BRAKES
The ABS brake system performs several self-tests
every time the ignition switch is turned on and the
vehicle is driven. The CAB monitors the systems
input and output circuits to verify the system is oper-
ating correctly. If the on board diagnostic system
senses that a circuit is malfunctioning the system
will set a trouble code in its memory.
NOTE: An audible noise may be heard during the
self-test. This noise should be considered normal.
NOTE: The MDS or DRB III scan tool is used to
diagnose the ABS system. For additional informa-
tion refer to the Antilock Brake section in Group
8W. For test procedures refer to the Chassis Diag-
nostic Manual.
STANDARD PROCEDURE
STANDARD PROCEDURE - RWAL SERVICE
PRECAUTIONS
The RWAL uses an electronic control module, the
CAB. This module is designed to withstand normal
current draws associated with vehicle operation.
Care must be taken to avoid overloading the CAB
circuits.In testing for open or short circuits, do
not ground or apply voltage to any of the cir-
cuits unless instructed to do so for a diagnostic
procedure.These circuits should only be tested
using a high impedance multi-meter or the DRB
tester as described in this section. Power should
never be removed or applied to any control module
with the ignition in the ON position. Before removing
or connecting battery cables, fuses, or connectors,
always turn the ignition to the OFF position.
CAUTION: Use only factory wiring harnesses. Do
not cut or splice wiring to the brake circuits. The
addition of after-market electrical equipment (car
phone, radar detector, citizen band radio, trailer
lighting, trailer brakes, ect.) on a vehicle equipped
with antilock brakes may affect the function of the
antilock brake system.
STANDARD PROCEDURE - BLEEDING ABS
BRAKE SYSTEM
ABS system bleeding requires conventional bleed-
ing methods plus use of the DRB scan tool. The pro-
cedure involves performing a base brake bleeding,
followed by use of the scan tool to cycle and bleed the
5 - 36 BRAKES - ABSBR/BE
BRAKES - ABS (Continued)

FRONT WHEEL SPEED
SENSOR
DESCRIPTION
The ABS brake system uses 3 wheel speed sensors.
A sensor is mounted to each front steering knuckles.
The third sensor is mounted on top of the rear axle
differential housing.
OPERATION
The Wheel Speed Sensor consists of a magnet sur-
rounded by windings from a single strand of wire.
The sensor sends a small AC signal to the CAB. This
signal is generated by magnetic induction. The mag-
netic induction is created when a toothed sensor ring
(exciter ring or tone wheel) passes the stationary
magnetic WSS.
When the ring gear is rotated, the exciter ring
passes the tip of the WSS. As the exciter ring tooth
approaches the tip of the WSS, the magnetic lines of
force expand, causing the magnetic field to cut across
the sensor's windings. This, in turn causes current to
flow through the WSS circuit (Fig. 2) in one direc-
tion. When the exciter ring tooth moves away from
the sensor tip, the magnetic lines of force collapse
cutting the winding in the opposite direction. This
causes the current to flow in the opposite direction.
Every time a tooth of the exciter ring passes the tip
of the WSS, an AC signal is generated. Each AC sig-
nal (positive to negative signal or sinewave) is inter-
preted by the CAB. It then compares the frequency of
the sinewave to a time value to calculate vehicle
speed. The CAB continues to monitor the frequency
to determine a deceleration rate that would indicate
a possible wheel-locking tendency.
The signal strength of any magnetic induction sen-
sor is directly affected by:
²Magnetic field strength; the stronger the mag-
netic field, the stronger the signal
²Number of windings in the sensor; more wind-
ings provide a stronger signal
²Exciter ring speed; the faster the exciter ring/
tone wheel rotates, the stronger the signal will be
²Distance between the exciter ring teeth and
WSS; the closer the WSS is to the exciter ring/tone
wheel, the stronger the signal will be
The rear WSS is not adjustable. A clearance speci-
fication has been established for manufacturing toler-
ances. If the clearance is not within these
specifications, then either the WSS or other compo-
nents may be damaged. The clearance between the
WSS and the exciter ring is 0.005 ± 0.050 in.
The assembly plant performs a ªRolls Testº on
every vehicle that leaves the assembly plant. One of
the test performed is a test of the WSS. To properlytest the sensor, the assembly plant connects test
equipment to the Data Link Connector (DLC). This
connector is located to the right of the steering col-
umn and attached to the lower portion of the instru-
ment panel (Fig. 3). The rolls test terminal is spliced
to the WSS circuit. The vehicle is then driven on a
set of rollers and the WSS output is monitored for
proper operation.
Fig. 2 Operation of the Wheel Speed Sensor
1 - MAGNETIC CORE
2 - CAB
3 - AIR GAP
4 - EXCITER RING
5 - COIL
Fig. 3 Data Link Connector - Typical
1 - 16±WAY DATA LINK CONNECTOR
5 - 38 BRAKES - ABSBR/BE

During antilock braking, the solenoid valves are
opened and closed as needed. The valves are not
static. They are cycled rapidly and continuously to
modulate pressure and control wheel slip and decel-
eration.
During antilock braking, solenoid valve pressure
modulation occurs in three stages, pressure decrease,
pressure hold, and pressure increase. The valves are
all contained in the valve body portion of the HCU.
PRESSURE DECREASE
The inlet valve is closed and the outlet valve is
opened during the pressure decrease cycle.
A pressure decrease cycle is initiated when speed
sensor signals indicate high wheel slip at one or
more wheels. At this point, the CAB closes the inlet
to prevent the driver from further increasing the
brake pressure and locking the brakes. The CAB
then opens the outlet valve, which also opens the
return circuit to the accumulators. Fluid pressure is
allowed to bleed off (decrease) as needed to prevent
wheel lock.
Once the period of high wheel slip has ended, the
CAB closes the outlet valve and begins a pressure
increase or hold cycle as needed.
PRESSURE HOLD
Both solenoid valves are closed in the pressure
hold cycle. Fluid apply pressure in the control chan-
nel is maintained at a constant rate. The CAB main-
tains the hold cycle until sensor inputs indicate a
pressure change is necessary.
PRESSURE INCREASE
The inlet valve is open and the outlet valve is
closed during the pressure increase cycle. The pres-
sure increase cycle is used to counteract unequal
wheel speeds. This cycle controls re-application of
fluid apply pressure due to changing road surfaces or
wheel speed.
REMOVAL
(1) Disconnect battery negative cable.
(2) Push the harness connector locks to release the
locks, then remove the connectors from the CAB.
(3) Disconnect brake lines from HCU (Fig. 7).
(4) Remove the two mounting bolts on either side
of the assembly which attach the assembly to the
mounting bracket.
(5) Tilt the assembly upward were the brake lines
attach and remove the assembly from the mounting
bracket.
INSTALLATION
(1) Install the assembly into the mounting bracket.
(2) Install the mounting bolts and tighten to 12
N´m (102 in. lbs.).
(3) Connect the CAB harnesses.
(4) Connect the brake lines to the HCU. Tighten
brake line fittings to 19-23 N´m (170-200 in. lbs.).
(5) Connect battery.
(6) Bleed brake system, (Refer to 5 - BRAKES -
STANDARD PROCEDURE).
Fig. 7 Brake Lines
1 - BRAKE LINES
2 - HCU
BR/BEBRAKES - ABS 5 - 41
HCU (HYDRAULIC CONTROL UNIT) (Continued)

ENGINE COOLANT TEMP
SENSOR - 5.9L
DESCRIPTION
The Engine Coolant Temperature (ECT) sensor is
used to sense engine coolant temperature. The sensor
protrudes into an engine water jacket.
The ECT sensor is a two-wire Negative Thermal
Coefficient (NTC) sensor. Meaning, as engine coolant
temperature increases, resistance (voltage) in the
sensor decreases. As temperature decreases, resis-
tance (voltage) in the sensor increases.
OPERATION
At key-on, the Powertrain Control Module (PCM)
sends out a regulated 5 volt signal to the ECT sensor.
The PCM then monitors the signal as it passes
through the ECT sensor to the sensor ground (sensor
return).
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.
The PCM uses inputs from the ECT sensor for the
following calculations:
²for engine coolant temperature gauge operation
through CCD or PCI (J1850) communications
²Injector pulse-width
²Spark-advance curves
²ASD relay shut-down times
²Idle Air Control (IAC) motor key-on steps
²Pulse-width prime-shot during cranking
²O2 sensor closed loop times
²Purge solenoid on/off times
²EGR solenoid on/off times (if equipped)
²Leak Detection Pump operation (if equipped)
²Radiator fan relay on/off times (if equipped)²Target idle speed
REMOVAL
WARNING: HOT, PRESSURIZED COOLANT CAN
CAUSE INJURY BY SCALDING. COOLING SYSTEM
MUST BE PARTIALLY DRAINED BEFORE REMOV-
ING THE COOLANT TEMPERATURE SENSOR.
REFER TO GROUP 7, COOLING.
(1) Partially drain cooling system (Refer to 7 -
COOLING - STANDARD PROCEDURE).
(2) Remove air cleaner assembly.
(3) Disconnect electrical connector from sensor
(Fig. 14).
(4)Engines with air conditioning:When
removing the connector from sensor, do not pull
directly on wiring harness. Fabricate an L-shaped
hook tool from a coat hanger (approximately eight
inches long). Place the hook part of tool under the
connector for removal. The connector is snapped onto
the sensor. It is not equipped with a lock type tab.
(5) Remove sensor from intake manifold.
INSTALLATION
(1) Install sensor.
(2) Tighten to 6±8 N´m (55±75 in. lbs.) torque.
(3) Connect electrical connector to sensor. The sen-
sor connector is symmetrical (not indexed). It can be
installed to the sensor in either direction.
(4) Install air cleaner assembly.
(5) Refill cooling system (Refer to 7 - COOLING -
STANDARD PROCEDURE).
Fig. 13 Block HeaterÐDiesel Engine
1 - BLOCK HEATER
Fig. 14 Engine Coolant Temperature
1 - GENERATOR
2 - A/C COMPRESSOR
3 - ENGINE COOLANT TEMPERATURE SENSOR
4 - ELEC. CONN.
BR/BEENGINE 7 - 47
ENGINE BLOCK HEATER - 5.9L DIESEL (Continued)

ELECTRONIC CONTROL MODULES
TABLE OF CONTENTS
page page
CENTRAL TIMER MODULE
DESCRIPTION..........................1
OPERATION............................3
DIAGNOSIS AND TESTING - CENTRAL TIMER
MODULE.............................4
REMOVAL.............................5
INSTALLATION..........................6
COMMUNICATION
DESCRIPTION - CCD DATA BUS............6
OPERATION - CCD DATA BUS..............7
DIAGNOSIS AND TESTING - CCD DATA BUS . . 11
CONTROLLER ANTILOCK BRAKE
DESCRIPTION.........................11
OPERATION...........................11
REMOVAL.............................11
INSTALLATION.........................12
DATA LINK CONNECTOR
DESCRIPTION - DATA LINK CONNECTOR....12
OPERATION - DATA LINK CONNECTOR......12
ENGINE CONTROL MODULE
DESCRIPTION - ECM....................13
OPERATION - ECM.....................13
REMOVAL.............................14
INSTALLATION.........................14POWERTRAIN CONTROL MODULE
DESCRIPTION
DESCRIPTION - PCM..................15
DESCRIPTION - MODES OF OPERATION . . . 15
DESCRIPTION - 5 VOLT SUPPLIES.......17
DESCRIPTION - IGNITION CIRCUIT SENSE . 17
DESCRIPTION - POWER GROUNDS......17
DESCRIPTION - SENSOR RETURN.......17
DESCRIPTION - SIGNAL GROUND........17
OPERATION
OPERATION - PCM - GAS ENGINES.......18
OPERATION - DIESEL..................18
OPERATION - 5 VOLT SUPPLIES.........19
OPERATION - IGNITION CIRCUIT SENSE . . . 19
REMOVAL.............................19
INSTALLATION.........................20
HEATED SEAT MODULE
DESCRIPTION.........................20
OPERATION...........................20
DIAGNOSIS AND TESTING - HEATED SEAT
MODULE............................21
REMOVAL.............................23
INSTALLATION.........................23
CENTRAL TIMER MODULE
DESCRIPTION
Three versions of the Central Timer Module (CTM)
are available on this vehicle, a base version (Fig. 1),
a high-line version (Fig. 2), and a premium version.
Whichever version of the CTM the vehicle is
equipped with, it is concealed under the driver side
end of the instrument panel inboard of the instru-
ment panel steering column opening, where it is
secured to a stamped steel bracket that is integral to
the instrument panel armature. The CTM is enclosed
in a molded plastic housing with one (base) or two
(high-line/premium) integral external connector
receptacles that connect it to the vehicle electrical
system through one (base) or two (high-line/pre-
mium) take outs with connectors from the instru-
ment panel wire harness.
The base version of the CTM is used on base mod-
els of this vehicle. It is also sometimes referred to as
the Integrated Electronic Module (IEM). The base
version of the CTM combines the functions of achime module and an intermittent wipe module in a
single unit. The high-line version of the CTM is used
on high-line vehicles. The high-line CTM provides all
of the functions of the base version of the CTM, but
also is used to control and integrate many additional
electronic functions and features included on high-
line models. The premium version of the CTM is the
same as the high-line version, but is used only on
models equipped with the heated seat option.
The high-line and premium versions of the CTM
utilize integrated circuitry and information carried
on the Chrysler Collision Detection (CCD) data bus
network along with many hard wired inputs to mon-
itor many sensor and switch inputs throughout the
vehicle. In response to those inputs, the internal cir-
cuitry and programming of the CTM allow it to con-
trol and integrate many electronic functions and
features of the vehicle through both hard wired out-
puts and the transmission of electronic message out-
puts to other electronic modules in the vehicle over
the CCD data bus.
BR/BEELECTRONIC CONTROL MODULES 8E - 1

BUS BIAS AND TERMINATION
The voltage network used by the CCD data bus to
transmit messages requires both bias and termina-
tion. At least one electronic control module on the
data bus must provide a voltage source for the CCD
data bus network known as bus bias, and there must
be at least one bus termination point for the data bus
circuit to be complete. However, while bias and ter-
mination are both required for data bus operation,
they both do not have to be within the same elec-
tronic control module. The CCD data bus is biased to
approximately 2.5 volts. With each of the electronic
control modules wired in parallel to the data bus, all
modules utilize the same bus bias. Therefore, based
upon vehicle options, the data bus can accommodate
two or twenty electronic control modules without
affecting bus voltage.
The power supplied to the data bus is known as
bus biasing. Bus bias is provided through a series cir-
cuit. To properly bias the data bus circuits, a 5 volt
supply is provided through a 13 kilohm resistor to
the Bus (±) circuit (Fig. 6). Voltage from the Bus (±)
circuit flows through a 120 ohm termination resistor
to the Bus (+) circuit. The Bus (+) circuit is grounded
through another 13 kilohm resistor. While at least
one termination resistor is required for the system to
operate, most DaimlerChrysler systems use two. The
second termination resistor serves as a backup (Fig.
7). The termination resistor provides a path for the
bus bias voltage. Without a termination point, volt-
age biasing would not occur. Voltage would go to 5
volts on one bus wire and 0 volts on the other bus
wire.The voltage drop through the termination resistor
creates 2.51 volts on Bus (±), and 2.49 volts on Bus
(+). The voltage difference between the two circuits is
0.02 volts. When the data bus voltage differential is a
steady 0.02 volts, the CCD system is considered
ªidle.º When no input is received from any module
and the ignition switch is in the Off position for a
pre-programmed length of time, the bus data
becomes inactive or enters the ºsleep mode.º Elec-
tronic control modules that provide bus bias can be
programmed to ºwake upº the data bus and become
active upon receiving any predetermined input or
when the ignition switch is turned to the On posi-
tion.
BUS MESSAGING
The electronic control modules used in the CCD
data bus system contain microprocessors. Digital sig-
nals are the means by which microprocessors operate
internally and communicate messages to other micro-
processors. Digital signals are limited to two states,
voltage high or voltage low, corresponding to either a
one or a zero. Unlike conventional binary code, the
CCD data bus systems translate a small voltage dif-
ference as a one (1), and a larger voltage difference
as a zero (0). The use of the 0 and 1 is referred to as
binary coding. Each binary number is called a bit,
and eight bits make up a byte. For example:
01011101 represents a message. The controllers in
the multiplex system are able to send thousands of
these bytes strung together to communicate a variety
of messages. Through the use of binary data trans-
mission, all electronic control modules on the data
bus can communicate with each other.
The microprocessors in the CCD data bus system
translate the binary messages into Hexadecimal
Code (or Hex Code). Hex code is the means by which
microprocessors communicate and interpret mes-
sages. When fault codes are received by the DRBIIIt
scan tool, they are translated into text for display on
the DRBIIItscreen. Although not displayed by the
DRBIIItfor Body Systems, hex codes are shown by
the DRBIIItfor Engine System faults.
When the microprocessor signals the transceiver in
the CCD chip to broadcast a message, the transceiver
turns the current drivers On and Off, which cycles
the voltage on the CCD data bus circuits to corre-
spond to the message. At idle, the CCD system rec-
ognizes the 0.02 voltage differential as a binary bit 1.
When the current drivers are actuated, the voltage
differential from idle must increase by 0.02 volt for
the CCD system to recognize a binary bit 0 (Fig. 8).
The nominal voltage differential for a 0 bit is 0.100
volts. However, data bus voltage differentials can
range anywhere between 0.02 and 0.120 volt.
Fig. 6 Bus Biasing
8E - 8 ELECTRONIC CONTROL MODULESBR/BE
COMMUNICATION (Continued)

DIAGNOSIS AND TESTING - CCD DATA BUS
CCD BUS FAILURE
The CCD data bus can be monitored using the
DRBIIItscan tool. However, it is possible for the
data bus to pass all tests since the voltage parame-
ters will be in ªrangeª and false signals are being
sent. There are essentially 12 ªhard failuresª that
can occur with the CCD data bus:
²Bus Shorted to Battery
²Bus Shorted to 5 Volts
²Bus Shorted to Ground
²Bus (+) Shorted to Bus (±)
²Bus (±) and Bus (+) Open
²Bus (+) Open
²Bus (±) Open
²No Bus Bias
²Bus Bias Level Too High
²Bus Bias Level Too Low
²No Bus Termination
²Not Receiving Bus Messages Correctly
Refer to the appropriate diagnostic information for
details on how to diagnose these faults using a
DRBIIItscan tool.
BUS FAILURE VISUAL SYMPTOM DIAGNOSIS
The following visible symptoms or customer com-
plaints, alone or in combination, may indicate a CCD
data bus failure:
²Airbag Indicator and Malfunction Indicator
Lamp (MIL) Illuminated
²Instrument Cluster Gauges (All) Inoperative
²No Compass Mini-Trip Computer (CMTC) Oper-
ation (if equipped)
CONTROLLER ANTILOCK
BRAKE
DESCRIPTION
The Controller Antilock Brakes (CAB) is a micro-
processor which handles testing, monitoring and con-
trolling the ABS brake system operation (Fig. 10).
The CAB functions are:
²Perform self-test diagnostics.
²Monitor the RWAL brake system for proper oper-
ation.
²Control the RWAL valve solenoids.
NOTE: If the CAB needs to be replaced, the rear
axle type and tire revolutions per mile must be pro-
gramed into the new CAB. For axle type refer to
Group 3 Differential and Driveline. For tire revolu-
tions per mile,(Refer to 22 - TIRES/WHEELS/TIRES -
SPECIFICATIONS) . To program the CAB refer to the
Chassis Diagnostic Manual.
OPERATION
SYSTEM SELF-TEST
When the ignition switch is turned-on the micro-
processor RAM and ROM are tested. If an error
occurs during the test, a DTC will be set into the
RAM memory. However it is possible the DTC will
not be stored in memory if the error has occurred in
the RAM module were the DTC's are stored. Also it
is possible a DTC may not be stored if the error has
occurred in the ROM which signals the RAM to store
the DTC.
CAB INPUTS
The CAB continuously monitors the speed of the
differential ring gear by monitoring signals generated
by the rear wheel speed sensor. The CAB determines
a wheel locking tendency when it recognizes the ring
gear is decelerating too rapidly. The CAB monitors
the following inputs to determine when a wheel lock-
ing tendency may exists:
²Rear Wheel Speed Sensor
²Brake Lamp Switch
²Brake Warning Lamp Switch
²Reset Switch
²4WD Switch (If equipped)
CAB OUTPUTS
The CAB controls the following outputs for antilock
braking and brake warning information:
²RWAL Valve
²ABS Warning Lamp
²Brake Warning Lamp
REMOVAL
(1) Disconnect battery negative cable.
Fig. 10 RWAL CAB
1-RWALCAB
BR/BEELECTRONIC CONTROL MODULES 8E - 11
COMMUNICATION (Continued)

ENGINE CONTROL MODULE
DESCRIPTION - ECM
The ECM is bolted to the left side of the engine
behind the fuel filter (Fig. 14). It is a separate com-
ponent and can be serviced. The FPCM is internal to
the fuel injection pump (Fig. 15) and cannot be ser-
viced.
OPERATION - ECM
The main functions of the Engine Control Module
(ECM) and Fuel Injection Pump Control Module
(FPCM) are to electrically control the fuel system.
The Powertrain Control Module (PCM)does not
controlthe fuel system.
The ECM can adapt its programming to meet
changing operating conditions.If the ECM has
been replaced, flashed or re-calibrated, the
ECM must learn the Accelerator Pedal Position
Sensor (APPS) idle voltage. Failure to learn
this voltage may result in unnecessary diagnos-
tic trouble codes. Refer to ECM Removal/Instal-
lation for learning procedures.
The ECM receives input signals from various
switches and sensors. Based on these inputs, the
ECM regulates various engine and vehicle operations
through different system components. These compo-
nents are referred to asECM Outputs.The sensors
and switches that provide inputs to the ECM are
consideredECM Inputs.NOTE: ECM Inputs:
²Accelerator Pedal Position Sensor (APPS) Volts
²APPS Idle Validation Switches #1 and #2
²Battery voltage
²Camshaft Position Sensor (CMP)
²CCD bus (+) circuits
²CCD bus (-) circuits
²Crankshaft Position Sensor (CKP)
²Data link connection for DRB scan tool
²(FPCM) Fuel Injection Pump Control Module
²Engine Coolant Temperature (ECT) sensor
²Ground circuits
²Intake manifold Air Temperature (IAT) sensor
²Manifold Air Pressure Sensor (Boost Pressure
Sensor)
²Oil pressure sensor
²PCM
²Power Take Off (PTO)
²Power ground
²Sensor return
²Signal ground
²Water-In-Fuel (WIF) sensor
Fig. 14 Engine Control Module (ECM) Location
1 - ENGINE CONTROL MODULE (ECM)
2 - HEX HEADED BOLT
3 - 50-WAY CONNECTOR
4 - FUEL TRANSFER PUMP
5 - MOUNTING BOLTS (3)
Fig. 15 Fuel Injection Pump Control Module (FPCM)
Location
1 - FPCM ELECTRICAL CONNECTOR
2 - HIGH-PRESSURE FUEL LINES
3 - FITTINGS
4 - FUEL INJECTION PUMP
5 - FPCM
BR/BEELECTRONIC CONTROL MODULES 8E - 13

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 posi-
tion sensor.
ENGINE WARM-UP MODE
This is an Open Loop mode. During engine warm-
up, the PCM receives inputs from:
²Battery voltage
²Crankshaft position sensor
²Engine coolant temperature sensor
²Intake manifold air temperature sensor
²Manifold absolute pressure (MAP) sensor
²Throttle position sensor (TPS)
²Camshaft position sensor signal (in the distribu-
tor)
²Park/neutral switch (gear indicator signalÐauto.
trans. only)
²Air conditioning select signal (if equipped)
²Air conditioning request signal (if equipped)
Based on these inputs the following occurs:
²Voltage 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.
²The PCM adjusts engine idle speed through the
idle air control (IAC) motor and adjusts ignition tim-
ing.
²The 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.
²When engine has reached operating tempera-
ture, the PCM will begin monitoring O2S 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:
²Air conditioning select signal (if equipped)
²Air conditioning request signal (if equipped)
²Battery voltage
²Crankshaft position sensor
²Engine coolant temperature sensor
²Intake manifold air temperature sensor
²Manifold absolute pressure (MAP) sensor
²Throttle position sensor (TPS)²Camshaft position sensor signal (in the distribu-
tor)
²Battery voltage
²Park/neutral switch (gear indicator signalÐauto.
trans. only)
²Oxygen sensors
Based on these inputs, the following occurs:
²Voltage 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 turn-
ing the ground circuit to each individual injector on
and off.
²The 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.
²The PCM adjusts ignition timing by increasing
and decreasing spark advance.
²The 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:
²Air conditioning select signal (if equipped)
²Air conditioning request signal (if equipped)
²Battery voltage
²Engine coolant temperature sensor
²Crankshaft position sensor
²Intake manifold air temperature sensor
²Manifold absolute pressure (MAP) sensor
²Throttle position sensor (TPS)
²Camshaft position sensor signal (in the distribu-
tor)
²Park/neutral switch (gear indicator signalÐauto.
trans. only)
²Oxygen (O2S) sensors
Based on these inputs, the following occurs:
²Voltage 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.
²The PCM monitors the O2S sensor input and
adjusts air-fuel ratio. It also adjusts engine idle
speed through the idle air control (IAC) motor.
²The PCM adjusts ignition timing by turning the
ground path to the coil on and off.
²The 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.
8E - 16 ELECTRONIC CONTROL MODULESBR/BE
POWERTRAIN CONTROL MODULE (Continued)

ACCELERATION MODE
This is an Open Loop mode. The PCM recognizes
an abrupt increase in throttle position or MAP pres-
sure 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.
²Air conditioning select signal (if equipped)
²Air conditioning request signal (if equipped)
²Battery voltage
²Engine coolant temperature sensor
²Crankshaft position sensor
²Intake manifold air temperature sensor
²Manifold absolute pressure (MAP) sensor
²Throttle position sensor (TPS)
²Camshaft position sensor signal (in the distribu-
tor)
²Park/neutral switch (gear indicator signalÐauto.
trans. only)
²Vehicle 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 decelera-
tion 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.
²Battery voltage
²Crankshaft position sensor
²Engine coolant temperature sensor
²Intake manifold air temperature sensor
²Manifold absolute pressure (MAP) sensor
²Throttle position sensor (TPS)
²Camshaft position sensor signal (in the distribu-
tor)
During wide open throttle conditions, the following
occurs:
²Voltage is applied to the fuel injectors with the
ASD relay via the PCM. The PCM will then controlthe 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 addi-
tional fuel. This is done by adjusting injector pulse
width.
²The 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.
DESCRIPTION - 5 VOLT SUPPLIES
Two different Powertrain Control Module (PCM)
five volt supply circuits are used; primary and sec-
ondary.
DESCRIPTION - IGNITION CIRCUIT SENSE
This circuit ties the ignition switch to the Power-
train Control Module (PCM).
DESCRIPTION - POWER GROUNDS
The Powertrain Control Module (PCM) has 2 main
grounds. Both of these grounds are referred to as
power grounds. All of the high-current, noisy, electri-
cal devices are connected to these grounds as well as
all of the sensor returns. The sensor return comes
into the sensor return circuit, passes through noise
suppression, and is then connected to the power
ground.
The power ground is used to control ground cir-
cuits for the following PCM loads:
²Generator field winding
²Fuel injectors
²Ignition coil(s)
²Certain relays/solenoids
²Certain sensors
DESCRIPTION - SENSOR RETURN
The Sensor Return circuits are internal to the Pow-
ertrain Control Module (PCM).
Sensor Return provides a low±noise ground refer-
ence for all engine control system sensors. Refer to
Power Grounds for more information.
DESCRIPTION - SIGNAL GROUND
Signal ground provides a low noise ground to the
data link connector.
BR/BEELECTRONIC CONTROL MODULES 8E - 17
POWERTRAIN CONTROL MODULE (Continued)