power train control module DODGE RAM 1500 1998 2.G Workshop Manual

GROUP TAB LOCATOR
Introduction
0Lubrication & Maintenance
2Suspension
3Differential & Driveline
5Brakes
6Clutch
7Cooling
8AAudio/Video
8BChime/Buzzer
8EElectronic Control Modules
8FEngine Systems
8GHeated Systems
8HHorn
8IIgnition Control
8JInstrument Cluster
8LLamps
8MMessage Systems
8NPower Systems
8ORestraints
8PSpeed Control
8QVehicle Theft Security
8RWipers/Washers
8TNavigation/Telecommunication
8WWiring
9Engine
11Exhaust System
13Frame & Bumpers
14Fuel System
19Steering
21Transmission and Transfer Case
22Tires/Wheels
23Body
24Heating & Air Conditioning
25Emissions Control
Component and System Index
Service Manual Comment Forms (Rear of Manual)

OPERATION
OPERATION - COOLING SYSTEM
The cooling system regulates engine operating tem-
perature. It allows the engine to reach normal oper-
ating temperature as quickly as possible. It also
maintains normal operating temperature and pre-
vents overheating.
The cooling system also provides a means of heat-
ing the passenger compartment and cooling the auto-
matic transmission fluid (if equipped). The cooling
system is pressurized and uses a centrifugal water
pump to circulate coolant throughout the system.
All engines utilize an ambient overflow bottle for
coolant recovery/reserve.
An optional factory installed maximum duty cool-
ing package is available on most models. This pack-
age will provide additional cooling capacity for
vehicles used under extreme conditions such as
trailer towing in high ambient temperatures.
OPERATION - HOSE CLAMPS
The spring type hose clamp applies constant ten-
sion on a hose connection. To remove a spring type
hose clamp, only use constant tension clamp pliers
designed to compress the hose clamp.
DIAGNOSIS AND TESTING
DIAGNOSIS AND TESTINGÐON-BOARD
DIAGNOSTICS (OBD)
COOLING SYSTEM RELATED DIAGNOSTICS
The Engine Control Module (ECM) has been pro-
grammed to monitor certain cooling system compo-
nents:
²If the engine has remained cool for too long a
period, such as with a stuck open thermostat, a Diag-
nostic Trouble Code (DTC) can be set.
²If an open or shorted condition has developed in
the electronically controlled viscous fan clutch circuit,
a Diagnostic Trouble Code (DTC) can be set.
²If fan speed is not detected a DTC will be set.
²Coolant temperature sensor circuit problems can
set a DTC.
If the problem is sensed in a monitored circuit
often enough to indicated an actual problem, a DTC
is stored. The DTC will be stored in the ECM mem-
ory for eventual display to the service technician.
(Refer to 25 - EMISSIONS CONTROL - DESCRIP-
TION).
ACCESSING DIAGNOSTIC TROUBLE CODES
To read DTC's and to obtain cooling system data,
(Refer to 25 - EMISSIONS CONTROL - DESCRIP-
TION).
ERASING TROUBLE CODES
After the problem has been repaired, use the
DRBIIItscan tool to erase a DTC. Refer to the
appropriate Powertrain Diagnostic Procedures ser-
vice information for operation of the DRBIIItscan
tool.
DIAGNOSIS AND TESTING - COOLING SYSTEM
- TESTING FOR LEAKS
ULTRAVIOLET LIGHT METHOD
A leak detection additive is available through the
parts department that can be added to cooling sys-
tem. The additive is highly visible under ultraviolet
light (black light). Pour one ounce of additive into
cooling system. Place heater control unit in HEAT
position. Start and operate the engine until the radi-
ator upper hose is warm to the touch. Aim the com-
mercially available black light tool at the components
to be checked. If leaks are present, the black light
will cause the additive to glow a bright green color.
The black light can be used in conjunction with a
pressure tester to determine if any external leaks
exist (Fig. 5).
Fig. 4 Spring Clamp Size Location
1 - SPRING CLAMP SIZE LOCATION
DRCOOLING 7 - 5
COOLING (Continued)

OPERATION
The heater warms the engine coolant providing
easier engine starting and faster warm-up in low
temperatures. Connecting the power cord to a
grounded 110-120 volt AC electrical outlet with a
grounded three wire extension cord provides the elec-
tricity needed to heat the element.
REMOVAL
(1) Disconnect the battery negative cables.
(2) Drain coolant from radiator and cylinder block
(Refer to 7 - COOLING - STANDARD PROCE-
DURE).
(3) Unscrew the power cord retaining cap and dis-
connect cord from heater element.
(4) Using a suitable size socket, loosen and remove
the block heater element (Fig. 9).
INSTALLATION
(1) Clean and inspect the threads in the cylinder
block.
(2) Coat heater element threads with Mopart
Thread Sealer with Teflon.
(3) Screw block heater into cylinder block and
tighten to 55 N´m (41 ft. lbs.).
(4) Connect block heater cord and tighten retain-
ing cap.
(5) Fill cooling system with recommended coolant
(Refer to 7 - COOLING - STANDARD PROCE-
DURE).
(6) Start and warm the engine.
(7) Check block heater for leaks.
ENGINE COOLANT
TEMPERATURE SENSOR
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
Fig. 8 Engine Block Heater ± 5.9L Diesel Engine
1 - BLOCK HEATER
Fig. 9 Block Heater - 5.9L Diesel Engine
1 - BLOCK HEATER
7 - 38 ENGINEDR
ENGINE BLOCK HEATER - 5.9L DIESEL (Continued)

DIAGNOSIS AND TESTINGÐTHERMOSTAT
ON-BOARD DIAGNOSTICS
Allgasoline powered modelsare equipped with
On-Board Diagnostics for certain cooling system com-
ponents. Refer to On-Board Diagnostics (OBD) in the
Diagnosis section of this group for additional infor-
mation. If the powertrain control module (PCM)
detects low engine coolant temperature, it will record
a Diagnostic Trouble Code (DTC) in the PCM mem-
ory. Do not change a thermostat for lack of heat as
indicated by the instrument panel gauge or by poor
heater performance unless a DTC is present. Refer to
the Diagnosis section of this group for other probable
causes.
The DTC can also be accessed through the
DRBIIItscan tool. Refer to the appropriate Power-
train Diagnostic Procedures information for diagnos-
tic information and operation of the DRBIIItscan
tool.
REMOVAL
WARNING: DO NOT LOOSEN THE RADIATOR
DRAINCOCK WITH THE COOLING SYSTEM HOT
AND PRESSURIZED. SERIOUS BURNS FROM THE
COOLANT CAN OCCUR.Do not waste reusable coolant. If the solution is
clean, drain the coolant into a clean container for
reuse.
If the thermostat is being replaced, be sure that
the replacement is the specified thermostat for the
vehicle model and engine type.
Factory installed thermostat housings on 5.9L
engine is installed on a gasket with an anti-stick
coating. This will aid in gasket removal and clean-up.
(1) Disconnect the negative battery cable.
(2) Drain the cooling system until the coolant level
is below the thermostat (Refer to 7 - COOLING -
STANDARD PROCEDURE).
(3) Air Conditioned vehicles: Remove the support
bracket (generator mounting bracket-to-intake mani-
fold) located near the rear of the generator (Fig. 17).
NOTE: On air conditioning equipped vehicles, the
generator must be partially removed.
(4) Remove the accessory drive belt (Refer to 7 -
COOLING/ACCESSORY DRIVE/DRIVE BELTS -
REMOVAL) (Fig. 18).
(5) Remove the generator mounting bolts. Do not
remove any of the wiring at the generator. If
equipped with 4WD, unplug the 4WD indicator lamp
wiring harness (located near rear of generator).
(6) Remove the generator. Position the generator
to gain access for the thermostat gasket removal.
WARNING: CONSTANT TENSION HOSE CLAMPS
ARE USED ON MOST COOLING SYSTEM HOSES.
WHEN REMOVING OR INSTALLING, USE ONLY
TOOLS DESIGNED FOR SERVICING THIS TYPE OF
CLAMP. ALWAYS WEAR SAFETY GLASSES WHEN
SERVICING CONSTANT TENSION CLAMPS.
Fig. 16 Thermostat - 5.7L/5.9L Gas Powered
Engines
1 - THERMOSTAT HOUSING
2 - GASKET
3 - INTAKE MANIFOLD
4 - THERMOSTAT
5 - MACHINED GROOVE
Fig. 17 Generator Support Bracket ± 5.9L Engine
1 - IDLER PULLEY BUSHING
2 - A/C AND/OR GENERATOR MOUNTING BRACKET
3 - IDLER PULLEY
4 - SCREW AND WASHER
7 - 42 ENGINEDR
ENGINE COOLANT THERMOSTAT- 5.7L (Continued)

(7) Air Conditioned vehicles; Install the generator.
Tighten the bolts to 41 N´m (30 ft. lbs.).
(8) Install the support bracket (generator mount-
ing bracket-to-intake manifold). (Fig. 17). Tighten the
bolts to 54 N´m (40 ft. lbs.).
(9) Install the accessory drive belt (Fig. 18)(Refer
to 7 - COOLING/ACCESSORY DRIVE/DRIVE
BELTS - INSTALLATION).
(10) Fill the cooling system (Refer to 7 - COOLING
- STANDARD PROCEDURE).
(11) Connect battery negative cable.
(12) Start and warm the engine. Check for leaks.
ENGINE COOLANT
THERMOSTAT - 3.7L/4.7L
DESCRIPTION
CAUTION: Do not operate the engine without a ther-
mostat, except for servicing or testing.
A pellet-type thermostat controls the operating
temperature of the engine by controlling the amount
of coolant flow to the radiator. On all engines the
thermostat is closed below 195ÉF (90ÉC). Above this
temperature, coolant is allowed to flow to the radia-
tor. This provides quick engine warm up and overall
temperature control. On the 3.7L4.7L engine the
thermostat is designed to block the flow of the cool-
ant bypass journal by 50% instead of completely
blocking the flow. This design controls coolant tem-
perature more accurately (Fig. 23).The same thermostat is used for winter and sum-
mer seasons. An engine should not be operated with-
out a thermostat, except for servicing or testing.
Operating without a thermostat causes other prob-
lems. These are: longer engine warmup time, unreli-
able warmup performance, increased exhaust
emissions and crankcase condensation. This conden-
sation can result in sludge formation.
OPERATION
The wax pellet is located in a sealed container at
the spring end of the thermostat. When heated, the
pellet expands, overcoming closing spring tension
and water pump pressure to force the valve to open.
DIAGNOSIS AND TESTINGÐTHERMOSTAT
ON-BOARD DIAGNOSTICS
Allgasoline powered modelsare equipped with
On-Board Diagnostics for certain cooling system com-
ponents. Refer to On-Board Diagnostics (OBD) in the
Diagnosis section of this group for additional infor-
mation. If the powertrain control module (PCM)
detects low engine coolant temperature, it will record
a Diagnostic Trouble Code (DTC) in the PCM mem-
ory. Do not change a thermostat for lack of heat as
Fig. 21 Thermostat PositionÐ5.9L EnginesFig. 22 Belt Routing ± 5.9L Engines
1 - IDLER PULLEY
2 - GENERATOR PULLEY
3 - A/C COMPRESSOR PULLEY
4 - IF W/OUT A/C
5 - POWER STEERING PUMP PULLEY
6 - WATER PUMP PULLEY
7 - CRANKSHAFT PULLEY
8 - AUTOMATIC TENSIONER
7 - 44 ENGINEDR
ENGINE COOLANT THERMOSTAT- 5.7L (Continued)

(7) Start the engine and check for coolant leaks.
Run engine to check for proper thermostat operation.
ENGINE COOLANT
THERMOSTAT - 8.0L
DESCRIPTION
CAUTION: Do not operate an engine without a ther-
mostat, except for servicing or testing.
The thermostat on all gas powered engines is
located beneath the thermostat housing at the front
of the intake manifold (Fig. 27).
The thermostat is a moveable sleeve type.
Coolant leakage into the pellet container will cause
the thermostat to fail in the open position. Thermo-
stats very rarely stick. Do not attempt to free a ther-
mostat with a prying device.
The same thermostat is used for winter and sum-
mer seasons. An engine should not be operated with-
out a thermostat, except for servicing or testing.
Operating without a thermostat causes longer engine
warmup time, unreliable warmup performance,
increased exhaust emissions and crankcase condensa-
tion that can result in sludge formation.
OPERATION
The wax pellet is located in a sealed container at
the spring end of the thermostat. When heated, the
pellet expands, overcoming closing spring tension
and water pump pressure to force the valve to open.
DIAGNOSIS AND TESTING - THERMOSTAT
ON-BOARD DIAGNOSTICS
Allgasoline powered modelsare equipped with
On-Board Diagnostics for certain cooling system com-
ponents. Refer to On-Board Diagnostics (OBD) in the
Diagnosis section of this group for additional infor-
mation. If the powertrain control module (PCM)
detects low engine coolant temperature, it will record
a Diagnostic Trouble Code (DTC) in the PCM mem-
ory. Do not change a thermostat for lack of heat as
indicated by the instrument panel gauge or by poor
heater performance unless a DTC is present. Refer to
the Diagnosis section of this group for other probable
causes. For other DTC numbers, (Refer to 25 - EMIS-
SIONS CONTROL - DESCRIPTION).
Fig. 26 Thermostat Removal/Installation
1 - THERMOSTAT HOUSING
2 - CYLINDER HEAD
3 - THERMOSTAT
Fig. 27 Thermostat - 8.0L V-10 Engine
1 - COOLANT TEMP. SENSOR (FOR PCM)
2 - HEATER SUPPLY FITTING
3 - BOLTS (6)
4 - HOUSING WITH INTEGRAL SEAL
5 - THERMOSTAT
6 - RUBBER LIP SEAL
7 - TEMP. GAUGE SENDING UNIT
7 - 48 ENGINEDR
ENGINE COOLANT THERMOSTAT - 5.9L DIESEL (Continued)

REMOTE RADIO SWITCH TEST TABLE
Switch Switch Position Resistance
Right
(White)Volume Up1.210 Kilohms
 1%
Right
(White)Volume Down3.010 Kilohms
 1%
Right
(White)Mode Advance0.0511 Kilohms
 1%
Left
(Black)Seek Up0.261 Kilohms
 1%
Left
(Black)Seek Down0.681 Kilohms
 1%
Left
(Black)Pre-Set Station
Advance0.162 Kilohms
 1%
(3) Reconnect the battery negative cable. Turn the
ignition switch to the On position. Check for 5 volts
at the radio control mux circuit cavities of the steer-
ing wheel wire harness connectors for both remote
radio switches. If OK, go to Step 4. If not OK, repair
the open or shorted radio control mux circuit to the
Integrated Power Module (IPM) as required.
(4) Disconnect and isolate the battery negative
cable. Disconnect the 22-way instrument panel wire
harness connector from the IPM. Check for continu-
ity between the remote radio switch ground circuit
cavities of the steering wheel wire harness connec-
tors for both remote radio switches and a good
ground. There should be no continuity. If OK, go to
Step 5. If not OK, repair the shorted remote radio
switch ground circuit to the IPM as required.
(5) Check for continuity between the remote radio
switch ground circuit cavities of the steering wheel
wire harness connectors for both remote radio
switches and the 22-way instrument panel wire har-
ness connector for the IPM. There should be continu-
ity. If OK, refer to the proper Diagnostic Procedures
manual to test the IPM and the PCI data bus. If not
OK, repair the open remote radio switch ground cir-
cuit as required.
REMOVAL
WARNING: DISABLE THE AIRBAG SYSTEM
BEFORE ATTEMPTING ANY STEERING WHEEL,
STEERING COLUMN, SEAT BELT TENSIONER, SIDE
AIRBAG, OR INSTRUMENT PANEL COMPONENT
DIAGNOSIS OR SERVICE. DISCONNECT AND ISO-
LATE THE BATTERY NEGATIVE (GROUND) CABLE,
THEN WAIT TWO MINUTES FOR THE AIRBAG SYS-
TEM CAPACITOR TO DISCHARGE BEFORE PER-
FORMING FURTHER DIAGNOSIS OR SERVICE. THIS
IS THE ONLY SURE WAY TO DISABLE THE AIRBAGSYSTEM. FAILURE TO TAKE THE PROPER PRE-
CAUTIONS COULD RESULT IN ACCIDENTAL AIR-
BAG DEPLOYMENT AND POSSIBLE PERSONAL
INJURY.
(1) Disconnect and isolate the battery negative
cable.
(2) Remove the driver airbag from the vehicle
(Refer to 8 - ELECTRICAL/RESTRAINTS/DRIVER
AIRBAG - REMOVAL).
(3) Remove the speed control switches (Refer to 8 -
ELECTRICAL/SPEED CONTROL/SWITCH -
REMOVAL).
(4) Unplug the wire harness connector from the
remote radio switch(es).
(5) Depress the tabs on each side of each switch
and push the switch through the rear steering wheel
cover (Fig. 16).
INSTALLATION
WARNING: DISABLE THE AIRBAG SYSTEM
BEFORE ATTEMPTING ANY STEERING WHEEL,
STEERING COLUMN, SEAT BELT TENSIONER, SIDE
AIRBAG, OR INSTRUMENT PANEL COMPONENT
DIAGNOSIS OR SERVICE. DISCONNECT AND ISO-
LATE THE BATTERY NEGATIVE (GROUND) CABLE,
THEN WAIT TWO MINUTES FOR THE AIRBAG SYS-
TEM CAPACITOR TO DISCHARGE BEFORE PER-
FORMING FURTHER DIAGNOSIS OR SERVICE. THIS
IS THE ONLY SURE WAY TO DISABLE THE AIRBAG
SYSTEM. FAILURE TO TAKE THE PROPER PRE-
CAUTIONS COULD RESULT IN ACCIDENTAL AIR-
BAG DEPLOYMENT AND POSSIBLE PERSONAL
INJURY.
Fig. 16 REMOTE SWITCHES
1 - REMOTE SWITCH
2 - SPEED CONTROL SWITCH
3 - BOLT
8A - 12 AUDIO/VIDEODR
REMOTE SWITCHES (Continued)

ELECTRONIC CONTROL MODULES
TABLE OF CONTENTS
page page
COMMUNICATION
DESCRIPTION..........................1
OPERATION............................2
CONTROLLER ANTILOCK BRAKE
DESCRIPTION..........................3
OPERATION............................3
REMOVAL.............................3
INSTALLATION..........................3
DATA LINK CONNECTOR
DESCRIPTION - DATA LINK CONNECTOR.....3
OPERATION - DATA LINK CONNECTOR......3
ENGINE CONTROL MODULE
DESCRIPTION - ECM.....................3
OPERATION - ECM......................3
REMOVAL.............................4
INSTALLATION..........................4
FRONT CONTROL MODULE
DESCRIPTION..........................5
OPERATION............................5
DIAGNOSIS AND TESTING - FRONT
CONTROL MODULE....................5
REMOVAL.............................5
INSTALLATION..........................5
HEATED SEAT MODULE
DESCRIPTION..........................6
OPERATION............................6
DIAGNOSIS AND TESTING - HEATED SEAT
MODULE.............................6
REMOVAL.............................7
INSTALLATION..........................7
POWERTRAIN CONTROL MODULE
DESCRIPTION
DESCRIPTION - PCM...................7DESCRIPTION - MODES OF OPERATION....7
DESCRIPTION - 5 VOLT SUPPLIES.......10
DESCRIPTION - IGNITION CIRCUIT SENSE . 10
DESCRIPTION - POWER GROUNDS......10
DESCRIPTION - SENSOR RETURN.......10
OPERATION
OPERATION - PCM....................10
OPERATION - 5 VOLT SUPPLIES.........11
OPERATION - IGNITION CIRCUIT SENSE . . . 11
REMOVAL.............................12
INSTALLATION.........................12
SENTRY KEY IMMOBILIZER MODULE
DESCRIPTION.........................13
OPERATION...........................13
STANDARD PROCEDURE - PCM/SKIM
PROGRAMMING......................14
REMOVAL.............................15
INSTALLATION.........................15
TRANSFER CASE CONTROL MODULE
DESCRIPTION.........................16
OPERATION...........................16
TRANSMISSION CONTROL MODULE
DESCRIPTION.........................20
OPERATION...........................20
STANDARD PROCEDURE
STANDARD PROCEDURE - TCM QUICK
LEARN..............................23
STANDARD PROCEDURE - DRIVE LEARN . . 23
COMMUNICATION
DESCRIPTION
The DaimlerChrysler Programmable Communica-
tion Interface (PCI) data bus system is a single wire
multiplex system used for vehicle communications on
many DaimlerChrysler Corporation vehicles. Multi-
plexing is a system that enables the transmission of
several messages over a single channel or circuit. All
DaimlerChrysler vehicles use this principle for com-
munication between various microprocessor-based
electronic control modules. The PCI data bus exceeds
the Society of Automotive Engineers (SAE) J1850
Standard for Class B Multiplexing.Many of the electronic control modules in a vehicle
require information from the same sensing device. In
the past, if information from one sensing device was
required by several controllers, a wire from each con-
troller needed to be connected in parallel to that sen-
sor. In addition, each controller utilizing analog
sensors required an Analog/Digital (A/D) converter in
order to9read9these sensor inputs. Multiplexing
reduces wire harness complexity, sensor current
loads and controller hardware because each sensing
device is connected to only one controller, which
reads and distributes the sensor information to the
other controllers over the data bus. Also, because
each controller on the data bus can access the con-
troller sensor inputs to every other controller on the
DRELECTRONIC CONTROL MODULES 8E - 1

data bus, more function and feature capabilities are
possible.
In addition to reducing wire harness complexity,
component sensor current loads and controller hard-
ware, multiplexing offers a diagnostic advantage. A
multiplex system allows the information flowing
between controllers to be monitored using a diagnos-
tic scan tool. The DaimlerChrysler system allows an
electronic control module to broadcast message data
out onto the bus where all other electronic control
modules can9hear9the messages that are being sent.
When a module hears a message on the data bus
that it requires, it relays that message to its micro-
processor. Each module ignores the messages on the
data bus that are being sent to other electronic con-
trol modules.
OPERATION
Data exchange between modules is achieved by serial
transmission of encoded data over a single wire broad-
cast network. The wire colors used for the PCI data bus
circuits are yellow with a violet tracer, or violet with a
yellow tracer, depending upon the application. The PCI
data bus messages are carried over the bus in the form
of Variable Pulse Width Modulated (VPWM) signals.
The PCI data bus speed is an average 10.4 Kilo-bits per
second (Kbps). By comparison, the prior two-wire
Chrysler Collision Detection (CCD) data bus system is
designed to run at 7.8125 Kbps.
The voltage network used to transmit messages
requires biasing and termination. Each module on
the PCI data bus system provides its own biasing
and termination. Each module (also referred to as a
node) terminates the bus through a terminating
resistor and a terminating capacitor. There are two
types of nodes on the bus. The dominant node termi-
nates the bus througha1KWresistor and a 3300 pF
capacitor. The Powertrain Control Module (PCM) is
the only dominant node for the PCI data bus system.
A standard node terminates the bus through an 11
KW resistor and a 330 pF capacitor.
The modules bias the bus when transmitting a
message. The PCI bus uses low and high voltage lev-
els to generate signals. Low voltage is around zero
volts and the high voltage is about seven and one-
half volts. The low and high voltage levels are gener-
ated by means of variable-pulse width modulation to
form signals of varying length. The Variable Pulse
Width Modulation (VPWM) used in PCI bus messag-
ing is a method in which both the state of the bus
and the width of the pulse are used to encode bit
information. A9zero9bit is defined as a short low
pulse or a long high pulse. A9one9bit is defined as a
long low pulse or a short high pulse. A low (passive)
state on the bus does not necessarily mean a zero bit.
It also depends upon pulse width. If the width isshort, it stands for a zero bit. If the width is long, it
stands for a one bit. Similarly, a high (active) state
does not necessarily mean a one bit. This too depends
upon pulse width. If the width is short, it stands for
a one bit. If the width is long, it stands for a zero bit.
In the case where there are successive zero or one
data bits, both the state of the bus and the width of
the pulse are changed alternately. This encoding
scheme is used for two reasons. First, this ensures
that only one symbol per transition and one transi-
tion per symbol exists. On each transition, every
transmitting module must decode the symbol on the
bus and begin timing of the next symbol. Since tim-
ing of the next symbol begins with the last transition
detected on the bus, all of the modules are re-syn-
chronized with each symbol. This ensures that there
are no accumulated timing errors during PCI data
bus communication.
The second reason for this encoding scheme is to
guarantee that the zero bit is the dominant bit on
the bus. When two modules are transmitting simul-
taneously on the bus, there must be some form of
arbitration to determine which module will gain con-
trol. A data collision occurs when two modules are
transmitting different messages at the same time.
When a module is transmitting on the bus, it is read-
ing the bus at the same time to ensure message
integrity. When a collision is detected, the module
that transmitted the one bit stops sending messages
over the bus until the bus becomes idle.
Each module is capable of transmitting and receiv-
ing data simultaneously. The typical PCI bus mes-
sage has the following four components:
²Message Header- One to three bytes in length.
The header contains information identifying the mes-
sage type and length, message priority, target mod-
ule(s) and sending module.
²Data Byte(s)- This is the actual message that
is being sent.
²Cyclic Redundancy Check (CRC) Byte- This
byte is used to detect errors during a message trans-
mission.
²In-Frame Response (IFR) byte(s)-Ifa
response is required from the target module(s), it can
be sent during this frame. This function is described
in greater detail in the following paragraph.
The IFR consists of one or more bytes, which are
transmitted during a message. If the sending module
requires information to be received immediately, the
target module(s) can send data over the bus during
the original message. This allows the sending module
to receive time-critical information without having to
wait for the target module to access the bus. After
the IFR is received, the sending module broadcasts
an End of Frame (EOF) message and releases control
of the bus.
8E - 2 ELECTRONIC CONTROL MODULESDR
COMMUNICATION (Continued)

The PCI data bus can be monitored using the
DRBIIItscan tool. It is possible, however, for the bus
to pass all DRBIIIttests and still be faulty if the
voltage parameters are all within the specified range
and false messages are being sent.
CONTROLLER ANTILOCK
BRAKE
DESCRIPTION
The Controler Antilock Brake (CAB) is mounted to
the Hydraulic Control Unit (HCU) and operates the
ABS system (Fig. 1).
OPERATION
The CAB voltage source is through the ignition
switch in the RUN position. The CAB contains a self
check program that illuminates the ABS warning
light when a system fault is detected. Faults are
stored in a diagnostic program memory and are
accessible with the DRB III scan tool. ABS faults
remain in memory until cleared, or until after the
vehicle is started approximately 50 times. Stored
faults arenoterased if the battery is disconnected.
NOTE: If the CAB is being replaced with a new CAB
is must be reprogrammed with the use of a DRB III.
REMOVAL
(1) Remove the negative battery cable from the
battery.
(2) Pull up on the CAB harness connector release
and remove connector.
(3) Remove the CAB mounting bolts.
(4) Remove the pump connector from the CAB.
(5) Remove the CAB from the HCU.
INSTALLATION
NOTE: If the CAB is being replaced with a new CAB
is must be reprogrammed with the use of a DRB III.
(1) Install CAB to the HCU.
(2) Install the pump connector to the CAB.
(3) Install mounting bolts. Tighten to 2 N´m (16 in.
lbs.).
(4) Install the wiring harness connector to the
CAB and push down on the release to secure the con-
nector.
(5) Install negative battery cable to the battery.
DATA LINK CONNECTOR
DESCRIPTION - DATA LINK CONNECTOR
The Data Link Connector (DLC) is located at the
lower edge of the instrument panel near the steering
column.
OPERATION - DATA LINK CONNECTOR
The 16±way data link connector (diagnostic scan
tool connector) links the Diagnostic Readout Box
(DRB) scan tool or the Mopar Diagnostic System
(MDS) with the Powertrain Control Module (PCM).
ENGINE CONTROL MODULE
DESCRIPTION - ECM
The engine control module (ECM) for the 5.9L Die-
sel engine is bolted to the left side of the engine
below the intake manifold.
OPERATION - ECM
The main function of the Engine Control Module
(ECM) is to electrically control the fuel system. The
Powertrain Control Module (PCM)does notcontrol
the 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.
Fig. 1 HYDRAULIC CONTROL UNIT
1 - HYDRAULIC CONTROL UNIT
2 - MOUNTING BOLTS
DRELECTRONIC CONTROL MODULES 8E - 3
COMMUNICATION (Continued)