2003 JEEP GRAND CHEROKEE Body control module

BCM programming then performs those tasks and
provides features through both PCI data bus commu-
nication with other electronic modules and hard
wired outputs to a number of relays. These relays
provide the BCM with the ability to control numer-
ous high current accessory systems in the vehicle.
The BCM circuitry operates on battery current
received through fuses in the Junction Block (JB) on a
non-switched fused B(+) circuit, a fused ignition switch
output (start-run) circuit, and a fused ignition switch
output (run-accessory) circuit. This arrangement allows
the BCM to provide some features regardless of the
ignition switch position. The BCM circuitry is grounded
through the chassis beneath the center console.
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 DRBIIItscan
tool. Refer to the appropriate diagnostic information.
HARD WIRED INPUTS
The hard wired inputs to the BCM include the fol-
lowing:
²A/C switch signal
²Ambient temperature sensor signal
²Body control module flash enable
²Coolant level switch sense
²Door ajar switch sense (two circuits - one left
rear, and one right rear)
²Driver seat heater switch mux
²Fog lamp switch sense
²Fused B(+)
²Fused ignition switch output (run-acc)
²Fused ignition switch output (st-run)
²Ground (five circuits - two Z1, and three Z2)
²Hazard switch sense
²Headlamp switch mux
²High beam switch sense
²Hood ajar switch sense (export)
²Key-in ignition switch sense
²Liftgate ajar switch sense
²Liftgate courtesy disable
²Liftgate flip-up ajar switch sense
²Panel lamps dimmer signal
²Park lamp relay output
²Passenger seat heater switch mux
²PCI bus
²Radio control mux
²Rear window defogger switch sense
²Seat belt switch sense
²Ultralight sensor signal
²Washer fluid switch sense
²Washer pump switch sense
²Windshield wiper switch mux
²Wiper park switch sense
MESSAGING
The BCM uses the following messages received
from other electronic modules over the PCI data bus:
²Accessory Delay Control (DDM/PDM)
²Battery Temperature (PCM)
²Chime Request (EMIC, EVIC, SKIM)
²Cylinder Lock Switch Status (DDM)
²Door Ajar Status/Front Doors (DDM/PDM)
²Door Lock Status (DDM/PDM)
²Engine Model (PCM)
²Engine RPM (PCM)
²Engine Temperature (PCM)
²English/Metric Default (EMIC)
²Fuel Tank Level (PCM)
²Fuel Used/Injector Pulses (PCM)
²Panic Control (PDM)
²Programmable Features Preferences/Audible &
Optical Chirps/Headlamp Delay (EVIC)
²RKE Status (PDM)
²Vehicle Identification Number (PCM)
²Vehicle Speed (PCM)
The BCM provides the following messages to other
electronic modules over the PCI data bus:
²A/C Switch Status (PCM)
²Ambient Temperature Data (AZC/EVIC/PCM)
²Average/Instantaneous Fuel Economy (EVIC)
²Country Code (EMIC)
²Courtesy Lamp Status (DDM/PDM)
²Distance To Empty (EVIC)
²Elapsed Ignition On Timer (EVIC)
²English/Metric Status (EMIC)
²Front & Rear Door Ajar Status (EVIC)
²Front & Rear Fog Lamp Status (EMIC)
²Heated Seat Switch Status (HSM/MHSM)
²High Beam Status (EMIC)
²Ignition Off Timer (EVIC)
²Ignition Switch Position (DDM/PDM)
²Key-In Ignition Status (DDM/PDM)
²Low Beam Status (EMIC)
²Panel Lamp Status (AZC/EMIC/Radio)
²Rear Window Defogger Relay Status (DDM/
PDM)
²Remote Radio Switch Status (Radio)
²Seatbelt Status (EMIC/MHSM/MSM)
DIAGNOSIS AND TESTING - BODY CONTROL
MODULE
The hard wired inputs to and outputs from the
Body Control Module (BCM) may be diagnosed and
tested using conventional diagnostic tools and proce-
dures. Refer to the appropriate wiring information.
Conventional diagnostic methods may not prove
conclusive in the diagnosis of the BCM. In order to
obtain conclusive testing of the BCM, the Program-
mable Communications Interface (PCI) data bus net-
work and all of the electronic modules that provide
8E - 4 ELECTRONIC CONTROL MODULESWJ
BODY CONTROL MODULE (Continued)

inputs to or receive outputs from the BCM must also
be checked. The most reliable, efficient, and accurate
means to diagnose the BCM, the PCI data bus net-
work, and the electronic modules that provide inputs
to or receive outputs from the BCM requires the use
of a DRBIIItscan tool and the appropriate diagnostic
information. The DRBIIItscan tool can provide con-
firmation that the PCI data bus network is func-
tional, that all of the modules are sending and
receiving the proper messages over the PCI data bus,
and that the BCM is receiving the proper hard wired
inputs and responding with the proper hard wired
outputs needed to perform its many functions.
WARNING: ON VEHICLES EQUIPPED WITH AIR-
BAGS, DISABLE THE AIRBAG SYSTEM BEFORE
ATTEMPTING ANY STEERING WHEEL, STEERING
COLUMN, 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.
REMOVAL
WARNING: ON VEHICLES EQUIPPED WITH AIR-
BAGS, DISABLE THE AIRBAG SYSTEM BEFORE
ATTEMPTING ANY STEERING WHEEL, STEERING
COLUMN, 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.
(1) Disconnect and isolate the battery negative
cable.
(2) Remove the instrument panel fuse cover.(Refer
to 8 - ELECTRICAL/POWER DISTRIBUTION/FUSE
COVER - REMOVAL).
(3) Access and disconnect the instrument panel
wire harness connectors from the BCM (Fig. 3).
(4) Remove the mounting screws (Torx T-20) that
secure the BCM to the JB.(5) Pull the BCM straight out towards the dash
panel far enough to disconnect the integral BCM to
JB connector.
(6) Remove the BCM.INSTALLATION
WARNING: ON VEHICLES EQUIPPED WITH AIR-
BAGS, DISABLE THE AIRBAG SYSTEM BEFORE
ATTEMPTING ANY STEERING WHEEL, STEERING
COLUMN, 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.
(1) Position the Body Control Module (BCM) to its
mounting location (Fig. 3).
(2) Align the terminal pins of the BCM connector
with the connector on the JB.
(3) Engage the BCM integral connector into the
JB.
(4) Install the four screws. Tighten the screws to
2.2 N´m (20 in. lbs.).
Fig. 3 Body Control Module Remove/Install
1 - JUNCTION BLOCK
2 - SCREWS (4)
3 - BODY CONTROL MODULE
4 - FUSE COVER LOCATOR CHANNELS
5 - FUSE COVER MOUNTING SLOTS
6 - INSTRUMENT PANEL WIRE HARNESS CONNECTORS
WJELECTRONIC CONTROL MODULES 8E - 5
BODY CONTROL MODULE (Continued)

(5) Connect the two instrument panel wire harness
connectors to the BCM.
(6) Reinstall the instrument panel fuse cover to
the bottom of the BCM and JB unit. (Refer to 8 -
ELECTRICAL/POWER DISTRIBUTION/FUSE
COVER - INSTALLATION).
(7) Connect the battery negative cable.
COMMUNICATION
DESCRIPTION
The Programmable Communication Interface (PCI)
data bus system is a single wire multiplex system
used for vehicle communications. Multiplexing is a
system that enables the transmission of several mes-
sages over a single channel or circuit.
Many of the control modules in a vehicle require
information from the same sensing device. Multiplex-
ing 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.
A multiplex system allows the information flowing
between controllers to be monitored using a diagnos-
tic scan tool. This system allows a control module to
broadcast message data out onto the bus where all
other control modules can read the messages that are
being sent. When a module reads a message on the
data bus that it requires, it relays that message to
its microprocessor. Each module ignores the mes-
sages on the data bus that it dosen't recognize.
OPERATION
Data exchange between modules is achieved by
serial transmission of encoded data over a single wire
broadcast network. 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).
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. The Powertrain
Control Module (PCM) is the only dominant node for
the PCI data bus system.
The PCI bus uses low and high voltage levels to
generate signals. The voltage on the buss varies
between zero and seven and one-half volts. The lowand high voltage levels are generated by means of
variable-pulse width modulation to form signals of
varying length.
When a module is transmitting on the bus, it is
reading the bus at the same time to ensure message
integrity.
Each module is capable of transmitting and receiv-
ing data simultaneously.
The PCI data bus can be monitored using the
DRBIIItscan tool. It is possible 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. 4).
OPERATION
The CAB voltage is supplied by the ignition switch
in the RUN position. The CAB contains dual micro-
processors. A logic block in each microprocessor
receives identical sensor signals. These signals are
processed and compared simultaneously. 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 DRBIIItscan tool. ABS
faults remain in memory until cleared, or until after
the vehicle is started approximately 50 times. Stored
Fig. 4 Controller Antilock Brakes
1 - HCU
2 - MOTOR
3 - CAB
8E - 6 ELECTRONIC CONTROL MODULESWJ
BODY CONTROL MODULE (Continued)

DIAGNOSIS AND TESTING - DOOR MODULE
WARNING: ON VEHICLES EQUIPPED WITH AIR-
BAGS, DISABLE THE AIRBAG SYSTEM BEFORE
ATTEMPTING ANY STEERING WHEEL, STEERING
COLUMN, 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.
The hard wired inputs to and outputs from the
Driver Door Module (DDM) or the Passenger Door
Module (PDM) may be diagnosed and tested using
conventional diagnostic tools and procedures. It is
suggested that the proper operation of the inopera-
tive power window motor, power door lock motor,
power liftgate lock motor, power mirror motors, or
heated mirror grid be confirmed using jumper wires
to bypass the door module. If the inoperative compo-
nent operates when the door module is bypassed,
check the circuits between the component and the
door module, as well as the fused B(+) and ground
circuits of the door module for shorts or opens.
These conventional diagnostic methods may not
prove conclusive in the diagnosis of the DDM or the
PDM. In order to obtain conclusive testing of these
modules, the Programmable Communications Inter-
face (PCI) data bus network and all of the modules
that provide inputs to or receive outputs from the
door modules must also be checked. The most reli-
able, efficient, and accurate means to diagnose the
DDM, the PDM, the PCI data bus network, and the
modules that provide inputs to or receive outputs
from the door modules requires the use of a DRBIIIt
scan tool and the appropriate diagnostic information.
REMOVAL
(1) Disconnect and isolate the battery negative
cable.
(2) Remove the trim panel from the front door.
(Refer to 23 - BODY/DOOR - FRONT/TRIM PANEL -
REMOVAL).
(3) Remove the door module from the back of the
front door trim panel (Fig. 8).
(4) Remove the door module from the front door
trim panel.
INSTALLATION
(1) Position the door module onto the front door
trim panel.
(2) Install the door module to the back of the front
door trim panel (Fig. 8). Tighten the screws to 2.2
N´m (20 in. lbs.).
(3) Reinstall the trim panel onto the front door.
(Refer to 23 - BODY/DOOR - FRONT/TRIM PANEL -
INSTALLATION).
(4) Reconnect the battery negative cable.
MEMORY HEATED SEAT/
MIRROR MODULE
DESCRIPTION
There are two different modules that can be used
in the optional heated seat system. The Heated Seat
Module (HSM) is used on vehicles that are not
equipped with the optional Memory System. The
Memory Heated Seat Module (MHSM) is used on
vehicles that are equipped with the optional Memory
System and the optional heated seat system.Refer to
Memory Systemin Power Seat Systems for more
information on the memory system option.
The module is mounted on a bracket that is located
between the power seat track and the seat cushion
frame (Fig. 9). The HSM or MHSM is used to control
the heated seat system functions for both front seats.
The HSM or MHSM contains a central processing
unit that communicates with other modules on the
Fig. 8 Door Module Remove/Install
1 - FRONT DOOR TRIM PANEL
2 - SCREW (5)
3 - DOOR MODULE
8E - 10 ELECTRONIC CONTROL MODULESWJ
DOOR MODULE (Continued)

Programmable Communications Interface (PCI) data
bus network.
For diagnosis of the HSM, MHSM or the PCI data
bus, a DRBIIItscan tool and the proper Diagnostic
Procedures manual are recommended. The HSM or
MHSM cannot be repaired and, if faulty or damaged,
it must be replaced.
OPERATION
The MSM receives hard wired inputs from the
power seat switch and the potentiometers on each of
the driver side power seat motors. The MSM receives
messages over the PCI data bus from the Driver
Door Module (DDM) (memory switch status), the
Powertrain Control Module (PCM) (vehicle speed sta-
tus), and the Body Control Module (seat belt switch
status).The MSM will prevent the seat memory recall
function from being initiated if the driver side seat
belt is buckled, if the transmission gear selector lever
is not in the Park or Neutral positions, or if the vehi-
cle is moving.
DIAGNOSIS AND TESTING
DIAGNOSIS AND TESTING - HEATED SEAT
MODULE
Visually inspect the related wiring harness connec-
tors. Look for broken, bent, pushed out, or corroded
terminals. If any of the above conditions are present,
repair as necessary. If not, use a DRBIIItscan tool
and the proper Diagnostic Procedures Manual to test
the HSM or MHSM. For complete circuit diagrams,
refer toPower Seat Premium I/IIIin Wiring Dia-
grams.
REMOVAL
(1) Disconnect and isolate the battery negative
cable.
(2) Remove the driver side front bucket seat from
the power seat track unit. Refer toBucket Seat
Track Adjusterin Body for the procedure.
(3) Lift the heated seat module off of the power
seat track and disconnect the power seat wire har-
ness connectors (Fig. 10).
(4) Remove the module from the bracket.
Fig. 9 Heated Seat Module Remove/Install
1 - NUT (4)
2 - SEAT CUSHION FRAME
3 - POWER SEAT TRACK
4 - STUD (4)
5 - MODULE
6 - BRACKET
Fig. 10 Heated Seat Module Remove/Install
1 - NUT (4)
2 - SEAT CUSHION FRAME
3 - POWER SEAT TRACK
4 - STUD (4)
5 - MODULE
6 - BRACKET
WJELECTRONIC CONTROL MODULES 8E - 11
MEMORY HEATED SEAT/MIRROR MODULE (Continued)

INSTALLATION
(1) Install the MHSM,HSM into the bracket.
(2) Position the heated seat module and mounting
bracket onto the power seat track.
(3) Reconnect the power seat wiring harness con-
nectors to the heated seat module.
(4) Install the driver side front bucket seat onto
the power seat track unit (Refer to 23 - BODY/
SEATS/SEAT TRACK ADJUSTER - INSTALLA-
TION).
(5) Reconnect the battery negative cable.
NOTE: If the vehicle is equipped with the optional
Memory System, following installation, it will be
necessary to initialize the Memory Heated Seat
Module (MHSM). In order to function properly, the
MHSM must ªlearnº the sensor values of each of
the power seat motor position transducers in each
of the adjuster hard stop positions. This is done by
performing the ªReset Guard Bandº procedure
using a DRBIIITscan tool and the proper Diagnostic
Procedures manual.
WARNING: THE ªRESET GUARD BANDº PROCE-
DURE WILL CAUSE THE DRIVER SIDE FRONT
SEAT TO AUTOMATICALLY ADJUST TO EACH OF
ITS TRAVEL LIMITS. BE CERTAIN THAT NO ONE IS
SEATED IN THE VEHICLE AND THAT THERE IS
NOTHING IN THE VEHICLE THAT WILL OBSTRUCT
SEAT MOVEMENT. FAILURE TO OBSERVE THIS
WARNING COULD RESULT IN PERSONAL INJURIES
AND/OR VEHICLE DAMAGE.
POWERTRAIN CONTROL
MODULE
DESCRIPTION
DESCRIPTION - PCM
The Powertrain Control Module (PCM) is located
in the engine compartment (Fig. 11). The PCM is
referred to as JTEC.
MODES OF OPERATION
As input signals to the Powertrain Control Module
(PCM) change, the PCM adjusts its response to the
output devices. For example, the PCM must calculate
different injector pulse width and ignition timing for
idle than it does for wide open throttle (WOT).
The PCM will operate in two different modes:
Open Loop and Closed Loop.
During Open Loop modes, the PCM receives input
signals and responds only according to preset PCMprogramming. Input from the oxygen (O2S) sensors
is not monitored during Open Loop modes.
During Closed Loop modes, the PCM will monitor
the oxygen (O2S) sensors input. This input indicates
to the PCM whether or not the calculated injector
pulse width results in the ideal air-fuel ratio. This
ratio is 14.7 parts air-to-1 part fuel. By monitoring
the exhaust oxygen content through the O2S sensor,
the PCM can fine tune the injector pulse width. This
is done to achieve optimum fuel economy combined
with low emission engine performance.
The fuel injection system has the following modes
of operation:
²Ignition switch ON
²Engine start-up (crank)
²Engine warm-up
²Idle
²Cruise
²Acceleration
²Deceleration
²Wide open throttle (WOT)
²Ignition switch OFF
The ignition switch On, engine start-up (crank),
engine warm-up, acceleration, deceleration and wide
open throttle modes are Open Loop modes. The idle
and cruise modes, (with the engine at operating tem-
perature) are Closed Loop modes.
IGNITION SWITCH (KEY-ON) MODE
This is an Open Loop mode. When the fuel system
is activated by the ignition switch, the following
actions occur:
Fig. 11 PCM Location
1 - PCM
2 - COOLANT TANK
8E - 12 ELECTRONIC CONTROL MODULESWJ
MEMORY HEATED SEAT/MIRROR MODULE (Continued)

(2) If equipped, remove Transmission Control Mod-
ule (TCM).
(3) Remove coolant reserve/overflow tank.
(4) Remove cover over electrical connectors. Cover
snaps onto PCM.
(5) Carefully unplug three 32±way connectors at
PCM.
(6) Remove three PCM bracket-to-body mounting
nuts (Fig. 13).
(7) Remove PCM/PCM bracket assembly from
vehicle.
(8) Remove 3 PCM-to-PCM bracket bolts (screws)
(Fig. 14).
INSTALLATION
USE THE DRBIIItSCAN TOOL TO REPRO-
GRAM THE NEW POWERTRAIN CONTROL
MODULE (PCM) WITH THE VEHICLES ORIGI-
NAL IDENTIFICATION NUMBER (VIN) AND
THE VEHICLES ORIGINAL MILEAGE. IF THIS
STEP IS NOT DONE, A DIAGNOSTIC TROUBLE
CODE (DTC) MAY BE SET.
The PCM is located on the cowl panel in right/rear
side of engine compartment (Fig. 12).
(1) Check pins in three 32±way electrical connec-
tors for damage. Repair as necessary.
(2) Install PCM to its mounting bracket. Tighten
three mounting bolts to 3 N´m (25 in. lbs.) torque.
(3) Install PCM/PCM bracket to body. Install 3
nuts and tighten 9 N´m (80 in. lbs.) torque.
(4) Install three 32±way connectors.(5) Install cover over electrical connectors. Cover
snaps onto PCM.
(6) Install coolant reserve/overflow tank.
(7) If equipped, install Transmission Control Mod-
ule (TCM).
(8) Connect negative cable to battery.
(9) Use the DRBIIItscan tool to reprogram new
PCM with vehicles original Identification Number
(VIN) and original vehicle mileage.
SENTRY KEY IMMOBILIZER
MODULE
DESCRIPTION
The Sentry Key Immobilizer Module (SKIM) is the
primary component of the Sentry Key Immobilizer
System (SKIS) (Fig. 15). The SKIM is located in the
steering column, below the ignition lock cylinder
housing. The SKIM has an integral halo-like antenna
ring that extends from one side.
The SKIM cannot be adjusted or repaired. If faulty
or damaged, the entire SKIM unit must be replaced.
OPERATION
The Sentry Key Immobilizer Module (SKIM) con-
tains a Radio Frequency (RF) transceiver and a
microprocessor. The SKIM transmits RF signals to,
and receives RF signals from the Sentry Key tran-
Fig. 14 Powertrain Control Module (PCM) Mounting
Bracket
1 - PCM BRACKET
2 - PCM
3 - PCM-TO-BRACKET SCREWS (3)
Fig. 15 Sentry Key Immobilizer Module
1 - STEERING COLUMN
2 - SKIM
3 - MOUNTING SCREW
WJELECTRONIC CONTROL MODULES 8E - 17
POWERTRAIN CONTROL MODULE (Continued)

sponder through a tuned antenna ring integral to the
SKIM housing. If this antenna ring is not mounted
properly around the ignition lock cylinder housing,
communication problems between the SKIM and the
transponder may arise. These communication prob-
lems will result in Sentry Key transponder-related
faults. The SKIM also communicates over the Pro-
grammable Communications Interface (PCI) data bus
with the Powertrain Control Module (PCM), the Elec-
troMechanical Instrument Cluster (EMIC), the Body
Control Module (BCM), and/or the DRBIIItscan tool.
The SKIM retains in memory the ID numbers of
any Sentry Key transponder that is programmed into
it. A maximum of eight transponders can be pro-
grammed into the SKIM. For added system security,
each SKIM is programmed with a unique Secret Key
code. This code is stored in memory, sent over the
PCI data bus to the PCM, and is encoded to the tran-
sponder of every Sentry Key that is programmed into
the SKIM. Another security code, called a PIN, is
used to gain access to the SKIM Secured Access
Mode. The Secured Access Mode is required during
service to perform the SKIS initialization and Sentry
Key transponder programming procedures. The
SKIM also stores the Vehicle Identification Number
(VIN) in its memory, which it learns through a PCI
data bus message from the PCM during SKIS initial-
ization.
In the event that a SKIM replacement is required,
the Secret Key code can be transferred to the new
SKIM from the PCM using the DRBIIItscan tool
and the SKIS replacement procedure. Proper comple-
tion of the SKIS initialization will allow the existing
Sentry Keys to be programmed into the new SKIM so
that new keys will not be required. In the event that
the original Secret Key code cannot be recovered,
SKIM replacement will also require new Sentry
Keys. The DRBIIItscan tool will alert the technician
during the SKIS replacement procedure if new Sen-
try Keys are required.
When the ignition switch is turned to the On posi-
tion, the SKIM transmits an RF signal to the tran-
sponder in the ignition key. The SKIM then waits for
an RF signal response from the transponder. If the
response received identifies the key as valid, the
SKIM sends a valid key message to the PCM over
the PCI data bus. If the response received identifies
the key as invalid, or if no response is received from
the key transponder, the SKIM sends an invalid key
message to the PCM. The PCM will enable or disable
engine operation based upon the status of the SKIM
messages. It is important to note that the default
condition in the PCM is an invalid key; therefore, if
no message is received from the SKIM by the PCM,
the engine will be disabled and the vehicle immobi-
lized after two seconds of running.The SKIM also sends indicator light status mes-
sages to the EMIC over the PCI data bus to tell the
EMIC how to operate the SKIS indicator. This indi-
cator light status message tells the EMIC to turn the
indicator on for about three seconds each time the
ignition switch is turned to the On position as a bulb
test. After completion of the bulb test, the SKIM
sends indicator light status messages to the EMIC to
turn the indicator off, turn the indicator on, or to
flash the indicator on and off. If the SKIS indicator
lamp flashes or stays on solid after the bulb test, it
signifies a SKIS fault. If the SKIM detects a system
malfunction and/or the SKIS has become inoperative,
the SKIS indicator will stay on solid. If the SKIM
detects an invalid key or if a key transponder-related
fault exists, the SKIS indicator will flash. If the vehi-
cle is equipped with the Customer Learn transponder
programming feature, the SKIM will also send mes-
sages to the EMIC to flash the SKIS indicator lamp,
and to the BCM to generate a single audible chime
tone whenever the Customer Learn programming
mode is being utilized. (Refer to 8 - ELECTRICAL/
VEHICLE THEFT SECURITY - STANDARD PRO-
CEDURE - SENTRY KEY TRANSPONDER
PROGRAMMING).
The SKIS performs a self-test each time the igni-
tion switch is turned to the On position, and will
store fault information in the form of Diagnostic
Trouble Codes (DTC's) in SKIM memory if a system
malfunction is detected. The SKIM can be diagnosed,
and any stored DTC's can be retrieved using a
DRBIIItscan tool. Refer to the appropriate diagnos-
tic information.
REMOVAL
WARNING: ON VEHICLES EQUIPPED WITH AIR-
BAGS, DISABLE THE AIRBAG SYSTEM BEFORE
ATTEMPTING ANY STEERING WHEEL, STEERING
COLUMN, 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.
(1) Disconnect and isolate the battery negative
cable.
(2) Remove the steering column opening cover
from the instrument panel. (Refer to 23 - BODY/IN-
STRUMENT PANEL/STEERING COLUMN OPEN-
ING COVER - REMOVAL).
8E - 18 ELECTRONIC CONTROL MODULESWJ
SENTRY KEY IMMOBILIZER MODULE (Continued)