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 and the SKIM are replaced at the

same time perform the following steps in order:

(1) Program the new PCM.
(2) Program the new SKIM.

(3) Replace all ignition keys and program them to

the new SKIM.

PROGRAMMING THE PCM

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
scan tool. 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 scan tool 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 scan tool will ask, Is odometer reading

between XX and XX? Select the YES or NO button on
the scan tool. If NO is selected, the scan tool 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 scan tool 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 scan tool 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

scan tool will display one of the following messages:

Programming Not Attempted - The scan tool

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 scan tool, 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.

8E - 2

ELECTRONIC CONTROL MODULES

ELECTRONIC CONTROL MODULES (Continued)

ANTILOCK BRAKE MODULE

DESCRIPTION

The Antilock Brake Module (ABM) 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 or when
in a traction control situation. The ABM utilizes a
47-way electrical connector on the vehicle wiring har-
ness. The power source for the ABM is through the
ignition switch in the RUN or ON position.

The ABM is mounted to the HCU as part of the

Integrated Control Unit (ICU) (Fig. 1). The ICU is
located in the engine compartment on the inboard
side of the left body frame rail. For information on
the ICU, (Refer to 5 - BRAKES/HYDRAULIC/ME-
CHANICAL/ICU (INTEGRATED CONTROL UNIT) -
DESCRIPTION).

OPERATION

The primary functions of the Antilock Brake Mod-

ule (ABM) are to:

• monitor the Antilock Brake System (ABS) for

proper operation.

• detect wheel locking or wheel slipping tenden-

cies by monitoring the speed of all four wheels of the
vehicle.

• control fluid modulation to the wheel brakes

while the system is in an ABS mode or the traction
control system is activated.

• store diagnostic information.

• provide communication to the scan tool while in

diagnostic mode.

The ABM constantly monitors the antilock brake

system for proper operation. If the ABM detects a
fault, it will send a message to the mechanical
instrument cluster (MIC) instructing it to turn on the
amber ABS warning indicator lamp and disable the
antilock braking system. The normal base braking
system will remain operational.

The ABM continuously monitors the speed of each

wheel through the signals generated by the wheel
speed sensors to determine if any wheel is beginning
to lock. When a wheel locking tendency is detected,
the ABM commands the ABM command coils to actu-
ate. The ABM command coils then open and close the
valves in the HCU that modulate brake fluid pres-
sure in some or all of the hydraulic circuits. The
ABM continues to control pressure in individual
hydraulic circuits until a locking tendency is no
longer present.

The ABM contains a self-diagnostic program that

monitors the antilock brake system for system faults.
When a fault is detected, the amber ABS warning
indicator lamp is turned on and the fault diagnostic
trouble code (DTC) is then stored in a diagnostic pro-
gram memory. These DTC’s will remain in the ABM
memory even after the ignition has been turned off.
The DTC’s can be read and cleared from the ABM
memory by a technician using a scan tool. If not
cleared with a scan tool, the fault occurrence and
DTC will be automatically cleared from the memory
after the identical fault has not been seen during the
next 3,500 miles of vehicle operation.

ANTILOCK BRAKE MODULE INPUTS

• Wheel speed sensors (four)

• Brake lamp switch

• Ignition switch

• System relay voltage

• Ground

• Traction control lamp actuation

• Diagnostic communication (PCI)

ANTILOCK BRAKE MODULE OUTPUTS

• Amber ABS warning indicator lamp actuation

(through MIC)

• Red BRAKE warning indicator lamp actuation

(through MIC)

• Traction control lamp

• Diagnostic communication (PCI)

REMOVAL

Due to packaging and limited space it is necessary

to remove and disassemble the ICU to service the
Antilock Brake Module on this vehicle. (Refer to 5 -
BRAKES/HYDRAULIC/MECHANICAL/ICU

(INTE-

GRATED CONTROL UNIT) - REMOVAL)

Fig. 1 Mk25e ICU

1 - ANTILOCK BRAKE MODULE (ABM)
2 - HYDRAULIC CONTROL UNIT (HCU)
3 - PUMP/MOTOR

ELECTRONIC CONTROL MODULES

8E - 3

INSTALLATION

Due to packaging and limited space it is necessary

to install the Antilock Brake Module on the HCU,
then install the ICU on the vehicle as an assembly.
(Refer to 5 - BRAKES/HYDRAULIC/MECHANICAL/
ICU (INTEGRATED CONTROL UNIT) - ASSEM-
BLY)

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
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 scan tool.
Refer to the appropriate diagnostic information.

REMOVAL

The Junction Block and Body Control Module

(BCM) are attached to each other. After removal they
can be separated.

(1) Disconnect and isolate the remote battery neg-

ative cable from the terminal on the shock tower.

(2) Open the front driver’s door and remove end

cap.

(3) Remove power mirror switch bezel, radio bezel,

and small bezel on the right side of the steering col-
umn.

(4) Remove the left lower instrument panel trim.
(5) Remove silencer.
(6) Remove wire harness connectors from Junction

Block.

(7) Remove Junction Block three mounting screws.
(8) Remove

Junction

Block/BCM

pulling

straight down from the mounting bayonet.

(9) Disconnect BCM wire connectors and remove

the assembly.

(10) Remove Junction Block/BCM from vehicle.
(11) With the Junction Block/BCM removed from

the vehicle, separate the BCM from the Junction
Block by removing the four screws.

(12) Disconnect BCM from the Junction Block.
(13) Unsnap the remote keyless entry module from

the BCM.

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

NOTE: If BCM is replaced, the VTSS must be
enabled in the new BCM via the scan tool in order
to start the vehicle.

INSTALLATION

NOTE: If BCM is replaced, the VTSS must be
enabled in the new BCM via the scan tool in order
to start the vehicle.

(1) Snap the remote keyless entry module onto the

BCM.

(2) Connect BCM to the Junction Block.
(3) Connect the BCM and junction block together

with the four screws.

(4) Install the Junction Block/BCM into vehicle.
(5) Connect BCM wire connectors and install the

assembly onto instrument panel.

(6) Install the Junction Block/BCM by pushing

straight up.

(7) Install the Junction Block three mounting

screws.

8E - 4

ELECTRONIC CONTROL MODULES

ANTILOCK BRAKE MODULE (Continued)

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