NOTE: Before replacing the PCM for a failed driver,
control circuit or ground circuit, be sure to check
the related component/circuit integrity for failures
not detected due to a double fault in the circuit.
Most PCM driver/control circuit failures are caused
by internal component failures (i.e. relay and sole-
noids) and shorted circuits (i.e. pull-ups, drivers
and switched circuits). These failures are difficult to
detect when a double fault has occurred and only
one DTC has set.

When a PCM (SBEC) and the SKIM are replaced

at the same time perform the following steps in
order:

(1) Program the new PCM (SBEC)

(2) Program the new SKIM
(3) Replace all ignition keys and program them to

the new SKIM.

PROGRAMMING THE PCM (SBEC)

The SKIS Secret Key is an ID code that is unique

to each SKIM. This code is programmed and stored
in the SKIM, PCM and transponder chip (ignition
keys). When replacing the PCM it is necessary to
program the secret key into the new PCM using the
DRB III. Perform the following steps to program the
secret key into the PCM.

(1) Turn the ignition switch on (transmission in

park/neutral).

(2) Use the DRB III and select THEFT ALARM,

SKIM then MISCELLANEOUS.

(3) Select PCM REPLACED (GAS ENGINE).
(4) Enter secured access mode by entering the

vehicle four-digit PIN.

(5) Select ENTER to update PCM VIN.

ELECTRONIC CONTROL MODULES

8E - 1

NOTE: If three attempts are made to enter secure
access mode using an incorrect PIN, secured
access mode will be locked out for one hour. To
exit this lockout mode, turn the ignition to the RUN
position for one hour then enter the correct PIN.
(Ensure all accessories are turned off. Also monitor
the battery state and connect a battery charger if
necessary).

(6) Press ENTER to transfer the secret key (the

SKIM will send the secret key to the PCM).

(7) Press Page Back to get to the Select System

menu and select ENGINE, MISCELLANEOUS, and
SRI MEMORY CHECK.

(8) The DRB III will ask, Is odometer reading

between XX and XX? Select the YES or NO button on
the DRB III. If NO is selected, the DRB III will read,
Enter odometer Reading<From I.P. odometer>. Enter
the odometer reading from the Instrument Panel and
press ENTER.

PROGRAMMING THE SKIM

(1) Turn the ignition switch on (transmission in

park/neutral).

(2) Use the DRB III and select THEFT ALARM,

SKIM then MISCELLANEOUS.

(3) Select PCM REPLACED (GAS ENGINE).
(4) Program the vehicle four-digit PIN into SKIM.
(5) Select COUNTRY CODE and enter the correct

country.

NOTE: Be sure to enter the correct country code. If
the incorrect country code is programmed into
SKIM, the SKIM must be replaced.

(6) Select YES to update VIN (the SKIM will learn

the VIN from the PCM).

(7) Press ENTER to transfer the secret key (the

PCM will send the secret key to the SKIM).

(8) Program ignition keys to SKIM.

NOTE: If the PCM and the SKIM are replaced at the
same time, all vehicle keys will need to be replaced
and programmed to the new SKIM.

PROGRAMMING IGNITION KEYS TO THE SKIM

(1) Turn the ignition switch on (transmission in

park/neutral).

(2) Use the DRB III and select THEFT ALARM,

SKIM then MISCELLANEOUS.

(3) Select PROGRAM IGNITION KEY’S.
(4) Enter secured access mode by entering the

vehicle four-digit PIN.

NOTE: A maximum of eight keys can be learned to
each SKIM. Once a key is learned to a SKIM it (the
key) cannot be transferred to another vehicle.

If ignition key programming is unsuccessful, the

DRB III will display one of the following messages:

Programming

Not Attempted

The

DRB

III

attempts to read the programmed key status and
there are no keys programmed into SKIM memory.

Programming Key Failed (Possible Used Key From

Wrong Vehicle) - SKIM is unable to program key due
to one of the following:

• faulty ignition key transponder

• ignition key is programmed to another vehicle.
8 Keys Already Learned, Programming Not Done -

SKIM transponder ID memory is full.

(5) Obtain ignition keys to be programmed from

customer (8 keys maximum).

(6) Using the DRB III, erase all ignition keys by

selecting MISCELLANEOUS and ERASE ALL CUR-
RENT IGN. KEYS.

(7) Program all ignition keys.
Learned Key In Ignition - Ignition key transponder

ID is currently programmed in SKIM memory.

BODY CONTROL MODULE

DESCRIPTION

The Body Control Module (BCM) is concealed

below the driver side end of the instrument panel in
the passenger compartment, where it is secured to
the dash panel side of the Junction Block (JB).

The BCM utilizes integrated circuitry and informa-

tion carried on the Programmable Communications
Interface (PCI) data bus network along with many
hard wired inputs to monitor many sensor and
switch inputs throughout the vehicle. In response to
those inputs, the internal circuitry and programming
of the BCM allow it to control and integrate many
electronic functions and features of the vehicle
through both hard wired outputs and the transmis-
sion of electronic message outputs to other electronic
modules in the vehicle over the PCI data bus.

OPERATION

The Body Control Module (BCM) is designed to

control and integrate many of the electronic features
and functions of the vehicle. The microprocessor-
based BCM hardware and software monitors many
hard wired switch and sensor inputs as well as those
resources it shares with other electronic modules in
the vehicle through its communication over the PCI
data bus network. The internal programming and all
of these inputs allow the BCM microprocessor to
determine the tasks it needs to perform and their
priorities, as well as both the standard and optional
features that it should provide. The BCM program-
ming then performs those tasks and provides those
features through both PCI data bus communication

8E - 2

ELECTRONIC CONTROL MODULES

ELECTRONIC CONTROL MODULES (Continued)

with other electronic modules and through hard
wired low current outputs to a number of relays.
These relays provide the BCM with the ability to
control numerous high current accessory systems in
the vehicle.

The BCM monitors its own internal circuitry as

well as many of its input and output circuits, and
will store a Diagnostic Trouble Code (DTC) in elec-
tronic memory for any failure it detects. These DTCs
can be retrieved and diagnosed using a DRBIII

t scan

tool. Refer to the appropriate diagnostic information.

REMOVAL

(1) Remove the Junction Block/BCM from the vehi-

cle. Refer to Power Distribution Systems, Junction
Block, Removal and Installation.

(2) Remove the four BCM attaching screws from

the Junction Block.

(3) Disconnect BCM from the Junction Block.

NOTE: The Remote Keyless Entry (RKE) module is
attached to the BCM with three screws. This must
be transferred (if equipped) to the new BCM.

NOTE: If the BCM is replaced, the Vehicle Theft /
Security System (VTSS (if equipped) must be
enabled in the new BCM via the DRB lll

scan tool

in order to start the vehicle.

INSTALLATION

(1) Connect the BCM to the Junction Block.
(2) Install the four BCM attaching screws to the

Junction Block.

(3) Install the Junction Block/BCM into the vehi-

cle. Refer to Power Distribution Systems, Junction
Block, Removal and Installation.

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 - 3

BODY CONTROL 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 ANTILOCK
BRAKE

DESCRIPTION

The controller antilock brake (CAB) is a micropro-

cessor-based device which monitors the antilock
brake system (ABS) during normal braking and con-
trols it when the vehicle is in an ABS stop. The CAB
is mounted to the HCU as part of the integrated con-
trol unit (ICU) (Fig. 1). The CAB uses a 24-way elec-
trical connector on the vehicle wiring harness. The
power source for the CAB is through the ignition
switch in the RUN or ON position. The CAB is on
the PCI bus.

Fig. 1 INTEGRATED CONTROL UNIT (TYPICAL)

1 - PUMP/MOTOR
2 - HCU
3 - PUMP/MOTOR CONNECTOR
4 - CAB

8E - 4

ELECTRONIC CONTROL MODULES

COMMUNICATION (Continued)

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