Jeep XJ. Manual - part 144

SKIM also transfers the “Secret Key” code to the
memory of each of the Sentry Key transponders dur-
ing new key programming. The security code is used
by the assembly plant to access the SKIS for initial-
ization, or by the dealer technician to access the sys-
tem for service. The SKIM also stores in its memory
the Vehicle Identification Number (VIN), which it
learns through a CCD data bus message from the
PCM during initialization.

The SKIM and the PCM both use software that

includes a rolling code algorithm strategy, which
helps to reduce the possibility of unauthorized SKIS
disarming. The rolling code algorithm ensures secu-
rity by preventing an override of the SKIS through
the unauthorized substitution of the SKIM or the
PCM. However, the use of this strategy also means
that replacement of either the SKIM or the PCM
units will require a system initialization procedure to
restore system operation.

When the ignition switch is turned to the On or Start

positions, the SKIM transmits an RF signal to excite
the Sentry Key transponder. The SKIM then listens for
a return RF signal from the transponder of the Sentry
Key that is inserted in the ignition lock cylinder. If the
SKIM receives an RF signal with valid “Secret Key” and
transponder identification codes, the SKIM sends a
“valid key” message to the PCM over the CCD data bus.
If the SKIM receives an invalid RF signal or no
response, it sends “invalid key” messages to the PCM.
The PCM will enable or disable engine operation based
upon the status of the SKIM messages.

The SKIM also sends messages to the instrument

cluster over the CCD data bus network to control the
SKIS indicator lamp. The SKIM sends messages to the
instrument cluster to turn the lamp on for about three
seconds when the ignition switch is turned to the On
position as a bulb test. After completion of the bulb test,
the SKIM sends bus messages to keep the lamp off for a
duration of about one second. Then the SKIM sends
messages to turn the lamp on or off based upon the
results of the SKIS self-tests. If the SKIS indicator
lamp comes on and stays on after the bulb test, it indi-
cates that the SKIM has detected a system malfunction
and/or that the SKIS has become inoperative.

If the SKIM detects an invalid key when the ignition

switch is turned to the On position, it sends messages to
the instrument cluster to flash the SKIS indicator lamp.
The SKIM can also send messages to the instrument
cluster to flash the lamp and to generate a single audi-
ble chime tone. These functions serve as an indication
to the customer that the SKIS has been placed in its
“Customer Learn” programming mode. See Sentry Key
Immobilizer System Transponder Programming in this
group for more information on the “Customer Learn”
programming mode.

For diagnosis or initialization of the SKIM and the

PCM, a DRBIII

t scan tool and the proper Diagnostic

Procedures manual are required. The SKIM cannot
be repaired and, if faulty or damaged, the unit must
be replaced.

SENTRY KEY IMMOBILIZER TRANSPONDER

The Sentry Key Immobilizer System (SKIS) uses a

transponder that is integral to each of the two igni-
tion keys that are supplied with the vehicle when it
is shipped from the factory. The transponder chip is
insulated within a nylon mount inserted in the head
of the key, and invisible beneath a molded rubber cap
(Fig. 1).

Each Sentry Key transponder has a unique tran-

sponder identification code programmed into it by the
manufacturer. The Sentry Key Immobilizer Module
(SKIM) has a unique “Secret Key” code programmed
into it by the manufacturer. Each time a new Sentry
Key transponder is programmed, the SKIM learns
the transponder identification code from the tran-
sponder, and the transponder learns the “Secret Key”
code from the SKIM. Each of these codes is stored
within the transponder and in the nonvolatile mem-
ory of the SKIM. Therefore, blank keys for the SKIS
must be programmed and their transponder identifi-
cation codes must be learned by and stored in the
SKIM memory, in addition to being cut to match the
mechanical coding of the ignition lock cylinder. See
Sentry Key Immobilizer System Transponder Pro-
gramming in this group for more information.

Fig. 1 Sentry Key Immobilizer Transponder

1 – MOLDED CAP
2 – TRANSPONDER
3 – MOLDED CAP REMOVED
4 – SENTRY KEY

8Q - 2

VEHICLE THEFT/SECURITY SYSTEMS

DESCRIPTION AND OPERATION (Continued)

The Sentry Key transponder is within the range of

the SKIM transceiver antenna ring when it is inserted
in the ignition lock cylinder. When the ignition switch is
turned to the Start or On positions, the SKIM trans-
ceiver issues a Radio Frequency (RF) signal that excites
the transponder chip. The transponder chip responds by
issuing an RF signal containing its transponder identi-
fication code and the “Secret Key” code. The SKIM
transceiver compares the transponder codes with the
codes stored in its memory to determine whether a valid
key is in the ignition lock cylinder.

The Sentry Key transponder cannot be repaired

and, if faulty or damaged, it must be replaced.

SENTRY KEY IMMOBILIZER SYSTEM
INDICATOR LAMP

The Sentry Key Immobilizer System (SKIS) indica-

tor lamp gives an indication when the SKIS is faulty
or when the vehicle has been immobilized due to the
use of an invalid ignition key. The lamp is controlled
by the instrument cluster circuitry based upon mes-
sages received from the Sentry Key Immobilizer
Module (SKIM) on the Chrysler Collision Detection
(CCD) data bus.

The SKIM sends messages to the instrument clus-

ter to turn the lamp on for about three seconds when
the ignition switch is turned to the On position as a
bulb test. After completion of the bulb test, the SKIM
sends bus messages to keep the lamp off for a dura-
tion of about one second. Then the SKIM sends mes-
sages to the instrument cluster circuitry to turn the
lamp on or off based upon the results of the SKIS
self-tests. If the SKIS indicator lamp comes on and
stays on after the bulb test, it indicates that the
SKIM has detected a system malfunction and/or that
the SKIS has become inoperative.

If the SKIM detects an invalid key when the ignition

The SKIS indicator lamp uses a replaceable incan-

descent bulb and bulb holder on the instrument clus-
ter electronic circuit board. Refer to Group 8E -
Instrument Panel Systems for diagnosis and service
of a faulty SKIS indicator lamp. If the SKIS indicator
lamp comes on and stays on after the bulb test func-
tion, diagnosis of the SKIS should be performed with
a DRB scan tool and the proper Diagnostic Proce-
dures manual.

DIAGNOSIS AND TESTING

SENTRY KEY IMMOBILIZER SYSTEM

WARNING: ON VEHICLES EQUIPPED WITH AIRBAGS,
REFER TO GROUP 8M - PASSIVE RESTRAINT SYS-
TEMS BEFORE ATTEMPTING ANY STEERING WHEEL,
STEERING COLUMN, OR INSTRUMENT PANEL COM-
PONENT DIAGNOSIS OR SERVICE. FAILURE TO TAKE
THE PROPER PRECAUTIONS COULD RESULT IN
ACCIDENTAL AIRBAG DEPLOYMENT AND POSSIBLE
PERSONAL INJURY.

NOTE: The following tests may not prove conclu-
sive in the diagnosis of this system. The most reli-
able, efficient, and accurate means to diagnose the
Sentry Key Immobilizer System involves the use of
a DRB scan tool. Refer to the proper Diagnostic
Procedures manual for the procedures.

The Sentry Key Immobilizer System (SKIS) and

the Chrysler Collision Detection (CCD) data bus net-
work should be diagnosed using a DRB scan tool.
The DRB will allow confirmation that the CCD data
bus is functional, that the Sentry Key Immobilizer
Module (SKIM) is placing the proper messages on the
CCD data bus, and that the Powertrain Control Mod-
ule (PCM) and the instrument cluster are receiving
the CCD data bus messages. Refer to the proper
Diagnostic Procedures manual for the procedures.
Refer to 8W-39 - Vehicle Theft Security System in
Group 8W - Wiring Diagrams for complete circuit
descriptions and diagrams.

(1) Check the fuses in the fuseblock module. If OK,

go to Step 2. If not OK, repair the shorted circuit or
component as required and replace the faulty fuse.

(2) Disconnect and isolate the battery negative

cable. Unplug the wire harness connector at the
SKIM. Check for continuity between the ground cir-
cuit cavity of the SKIM wire harness connector and a
good ground. There should be continuity. If OK, go to
Step 3. If not OK, repair the open circuit to ground
as required.

(3) Connect the battery negative cable. Check for

battery voltage at the fused B(+) circuit cavity of the
SKIM wire harness connector. If OK, go to Step 4. If
not OK, repair the open circuit to the fuse in the
fuseblock module as required.

(4) Turn the ignition switch to the On position.

Check for battery voltage at the fused ignition switch
output (run/start) circuit cavity of the SKIM wire
harness connector. If OK, use a DRB scan tool and
the proper Diagnostic Procedures manual to complete
the diagnosis of the SKIS. If not OK, repair the open
circuit to the fuse in the fuseblock module as
required.

VEHICLE THEFT/SECURITY SYSTEMS

8Q - 3

DESCRIPTION AND OPERATION (Continued)

SERVICE PROCEDURES

SENTRY KEY IMMOBILIZER SYSTEM
TRANSPONDER PROGRAMMING

Two

programmed

Sentry

Key

transponders

are

included with the Sentry Key Immobilizer System
(SKIS) when it is shipped from the factory. The Sentry
Key Immobilizer Module (SKIM) can be programmed to
recognize up to six additional transponders, for a total
of eight Sentry Keys. The following “Customer Learn”
programming procedure for the programming of addi-
tional transponders requires access to at least two of
the valid Sentry Keys. If two valid Sentry Keys are not
available, Sentry Key programming will require the use
of a DRB scan tool and the proper Diagnostic Proce-
dures manual.

CUSTOMER LEARN

(1) Obtain the additional Sentry Key transponder

blank(s) that are to be programmed for the vehicle. Cut
the additional Sentry Key transponder blanks to match
the ignition lock cylinder mechanical key codes.

(2) Insert one of the two valid Sentry Key tran-

sponders into the ignition switch and turn the igni-
tion switch to the On position.

(3) After the ignition switch has been in the On posi-

tion for about three seconds, but no more than fifteen
seconds later, cycle the ignition switch back to the Off
position. Replace the first valid Sentry Key in the igni-
tion lock cylinder with the second valid Sentry Key and
turn the ignition switch back to the On position.

(4) About ten seconds after the completion of Step

3, the SKIS indicator lamp will start to flash and a
single audible chime tone will sound to indicate that
the system has entered the “Customer Learn” pro-
gramming mode.

(5) Within about fifty seconds of entering the “Cus-

tomer Learn” programming mode, turn the ignition
switch to the Off position, replace the valid Sentry
Key with a blank Sentry Key transponder, and turn
the ignition switch back to the On position.

(6) About ten seconds after the completion of Step

5, a single audible chime tone will sound and the
SKIS indicator lamp will stop flashing and stay on
solid for about three seconds to indicate that the
blank Sentry Key transponder has been successfully
programmed. The SKIS will immediately return to
normal system operation following exit from the
“Customer Learn” programming mode.

(7) Go back to Step 2 and repeat this process for

each additional Sentry Key transponder blank to be
programmed.

If any of the above steps is not completed in the

proper sequence, or within the allotted time, the SKIS
will automatically exit the “Customer Learn” program-
ming mode. The SKIS will also automatically exit the

“Customer Learn” programming mode if it sees a non-
blank Sentry Key transponder when it should see a
blank, if it has already programmed eight valid Sentry
Keys, or if the ignition switch is turned to the Off posi-
tion for more than about fifty seconds.

REMOVAL AND INSTALLATION

SENTRY KEY IMMOBILIZER MODULE

(1) Disconnect and isolate the battery negative

cable.

(2) Remove the knee blocker from the instrument

panel. See Knee Blocker in Group 8E - Instrument
Panel Systems for the procedures.

(3) Remove the three screws that secure the lower

steering column shroud to the upper shroud (Fig. 2).

Fig. 2 Steering Column Shrouds Remove/Install

1 – UPPER SHROUD
2 – SCREW (3)
3 – LOWER SHROUD
4 – STEERING WHEEL

8Q - 4

VEHICLE THEFT/SECURITY SYSTEMS

(4) If the vehicle is equipped with a standard non-

tilt steering column, loosen the two upper steering
column mounting nuts. If the vehicle is equipped
with the optional tilt steering column, move the tilt
steering column to the fully lowered position.

(5) Remove both the upper and lower shrouds from

the steering column.

(6) Disengage the steering column wire harness

retainer from the tab on the top of the Sentry Key
Immobilizer Module (SKIM) mounting bracket (Fig. 3).

(7) Unplug the wire harness connector from the

SKIM receptacle.

(8) The SKIM mounting bracket features a clip for-

mation that secures the SKIM to the inboard lower
flange of the steering column jacket. Pull downward
on the connector end of the SKIM mounting bracket
to release this clip from the steering column jacket.

(9) Rotate the SKIM and its mounting bracket

downwards and then to the side away from the steer-
ing column to slide the SKIM antenna ring from
around the ignition switch lock cylinder housing.

(10) Remove the SKIM from the vehicle.
(11) Reverse the removal procedures to install.

Tighten the non-tilt steering column mounting nuts
to 22 N·m (200 in. lbs.) and the steering column
shroud mounting screws to 2 N·m (18 in. lbs.).

NOTE: If the SKIM is replaced with a new unit, a
DRBIII

scan tool and the proper Diagnostic Proce-

dures manual MUST be used to initialize the new
SKIM and to program at least two Sentry Key
transponders.

Fig. 3 Sentry Key Immobilizer Module Remove/Install

1 – UPPER SHROUD
2 – STEERING COLUMN
3 – WIRE HARNESS CONNECTOR
4 – SENTRY KEY IMMOBILIZER MODULE

5 – IGNITION LOCK CYLINDER
6 – SCREW
7 – LOWER SHROUD
8 – STEERING WHEEL

VEHICLE THEFT/SECURITY SYSTEMS

8Q - 5

REMOVAL AND INSTALLATION (Continued)

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