Dodge Dakota (R1). Manual - part 289

repair the open fused B(+) circuit(s) between the
CTM and the PDC as required.

(4) Check the fused ignition switch output (run-

start) fuse (Fuse 11 - 10 ampere) and the fused igni-
tion switch output (run-acc) fuse (Fuse 5 - 20
ampere) in the Junction Block (JB). If OK, go to Step
5. If not OK, repair the shorted circuit or component
as required and replace the faulty fuse(s).

(5) Reconnect the battery negative cable. Turn the

ignition switch to the On position. Check for battery
voltage at the fused ignition switch output (run-start)
fuse (Fuse 11 - 10 ampere) and the fused ignition
switch output (run-acc) fuse (Fuse 5 - 20 ampere) in
the JB. If OK, go to Step 6. If not OK, repair the
open fused ignition switch output (run-start) circuit
or fused ignition switch output (run-acc) circuit
between the JB and the ignition switch as required.

(6) Turn the ignition switch to the Off position.

Disconnect and isolate the battery negative cable.
Disconnect the instrument panel wire harness con-
nector (Connector C1) for the CTM from the CTM
connector receptacle. Reconnect the battery negative
cable. Turn the ignition switch to the On position.
Check for battery voltage at the fused ignition switch
output (run-start) circuit cavity and the fused igni-
tion switch output (run-acc) cavity of the instrument
panel wire harness connector (Connector C1) for the
CTM. If OK, go to Step 7. If not OK, repair the open
fused ignition switch output (run-start) circuit or
fused ignition switch output (run-acc) circuit between
the CTM and the JB as required.

(7) Turn the ignition switch to the Off position.

Check for continuity between each of the three
ground circuits in the instrument panel wire harness
connector (Connector C1) for the CTM and a good
ground. In each case there should be continuity. If
OK, use a DRBIII

t scan tool to perform further diag-

nosis of the CTM. Refer to the appropriate diagnostic
information. If not OK, repair the open ground cir-
cuit(s) to ground (G207 or G208) as required.

REMOVAL

WARNING: ON VEHICLES EQUIPPED WITH AIR-
BAGS, DISABLE THE AIRBAG SYSTEM BEFORE
ATTEMPTING ANY STEERING WHEEL, STEERING
COLUMN, SEAT BELT TENSIONER, OR INSTRU-
MENT PANEL COMPONENT DIAGNOSIS OR SER-
VICE. DISCONNECT AND ISOLATE THE BATTERY
NEGATIVE (GROUND) CABLE, THEN WAIT TWO
MINUTES FOR THE AIRBAG SYSTEM CAPACITOR
TO DISCHARGE BEFORE PERFORMING FURTHER
DIAGNOSIS OR SERVICE. THIS IS THE ONLY SURE
WAY TO DISABLE THE AIRBAG SYSTEM. FAILURE
TO TAKE THE PROPER PRECAUTIONS COULD

RESULT IN ACCIDENTAL AIRBAG DEPLOYMENT
AND POSSIBLE PERSONAL INJURY.

NOTE: Before replacing a Central Timer Module
(CTM), use a DRBIII

scan tool to retrieve the cur-

rent settings for the CTM programmable features.
Refer to the appropriate diagnostic information.
These settings should be duplicated in the replace-
ment CTM using the DRBIII

scan tool before

returning the vehicle to service.

(1) Disconnect and isolate the battery negative

cable.

(2) Remove the trim from the left cowl side inner

panel. (Refer to 23 - BODY/INTERIOR/COWL TRIM
COVER - REMOVAL).

(3) Disconnect the two instrument panel wire har-

ness connectors and one body wire harness connector
from the CTM connector receptacles (Fig. 2).

(4) Remove the three screws that secure the CTM

to the left cowl side inner panel.

(5) Remove the CTM from the left cowl side inner

panel.

Fig. 2 Central Timer Module

1 - CENTRAL TIMER MODULE
2 - COWL SIDE INNER PANEL
3 - SCREW (3)
4 - BODY WIRE HARNESS CONNECTOR
5 - INSTRUMENT PANEL WIRE HARNESS CONNECTOR (2)

8E - 6

ELECTRONIC CONTROL MODULES

CENTRAL TIMER MODULE (Continued)

INSTALLATION

NOTE: Before replacing a Central Timer Module
(CTM), use a DRBIII

scan tool to retrieve the cur-

rent settings for the CTM programmable features.
Refer to the appropriate diagnostic information.
These settings should be duplicated in the replace-
ment high-line/premium CTM using the DRBIII

scan tool before returning the vehicle to service.

(1) Position the CTM onto the left cowl side inner

panel (Fig. 2).

(2) Install and tighten the three screws that secure

the CTM to the left cowl side inner panel. Tighten
the screws to 2 N·m (20 in. lbs.).

(3) Reconnect the two instrument panel wire har-

ness connectors and one body wire harness connector
to the CTM connector receptacles.

(4) Reinstall the trim onto the left cowl side inner

panel. (Refer to 23 - BODY/INTERIOR/COWL TRIM
COVER - INSTALLATION).

(5) Reconnect the battery negative cable.

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 to

9read9 these 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
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 can

9hear9 the 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
broadcast 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 appli-
cation. The PCI data bus messages are carried over
the bus in the form of Variable Pulse Width Modu-
lated (VPWM) signals. The PCI data bus speed is an
average 10.4 Kilo-bits per second (Kbps). By compar-
ison, 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 through a 1 KW resistor 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-

ELECTRONIC CONTROL MODULES

8E - 7

CENTRAL TIMER MODULE (Continued)

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. A

9zero9 bit is defined as a short low

pulse or a long high pulse. A

9one9 bit 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 is
short, 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:

• Message 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.

• Data Byte(s) - This is the actual message that

is being sent.

• Cyclic Redundancy Check (CRC) Byte - This

byte is used to detect errors during a message trans-
mission.

• In-Frame Response (IFR) byte(s) - If a

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.

The PCI data bus can be monitored using the

DRBIII

t scan tool. It is possible, however, for the bus

to pass all DRBIII

t tests and still be faulty if the

voltage parameters are all within the specified range
and false messages are being sent.

CONTROLLER REAR WHEEL
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. 3). The
CAB functions are:

• Perform self-test diagnostics.

• Monitor the RWAL brake system for proper oper-

ation.

• Control the RWAL valve solenoids.

Fig. 3 RWAL CAB

1 - RWAL CAB

8E - 8

ELECTRONIC CONTROL MODULES

COMMUNICATION (Continued)

The CAB is mounted on the top of the hydraulic

control unit (Fig. 4). The CAB operates the ABS sys-
tem and is separate from other vehicle electrical cir-
cuits. CAB voltage source is through the ignition
switch in the RUN position.

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.

The CAB contains a self check program that illu-

minates the ABS warning light when a system fault
is detected. Faults are stored in a diagnostic program
memory and are accessible with the DRB scan tool.

ABS faults remain in memory until cleared, or

until after the vehicle is started approximately 50
times. Stored faults are not erased if the battery is
disconnected.

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:

• Rear Wheel Speed Sensor

• Brake Lamp Switch

• Brake Warning Lamp Switch

• Reset Switch

• 4WD Switch (If equipped)

CAB OUTPUTS

The CAB controls the following outputs for antilock

braking and brake warning information:

• RWAL Valve

• ABS Warning Lamp

• Brake Warning Lamp

REMOVAL

(1) Push the CAB harness connector lock to

release the lock and remove the connector (Fig. 5)
from the controller.

(2) Remove the RWAL valve harness and the pump

motor connectors from the controller. (Fig. 6)

(3) Remove the controller mounting screws and

remove the controller from the mounting bracket
(Fig. 7).

Fig. 4 CAB/HCU

1 - CAB
2 - PUMP WIRING
3 - PUMP MOTOR
4 - HCU

ELECTRONIC CONTROL MODULES

8E - 9

CONTROLLER ANTILOCK BRAKE (Continued)

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