Jeep 200 Cherokee Service Manual page 578

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VEHICLE THEFT/SECURITY SYSTEMS
DESCRIPTION AND OPERATION
SENTRY KEY IMMOBILIZER SYSTEM . . . . . . . . . 1
SENTRY KEY IMMOBILIZER MODULE. . . . . . . . . 1
SENTRY KEY IMMOBILIZER TRANSPONDER . . . 2
SENTRY KEY IMMOBILIZER SYSTEM
INDICATOR LAMP . . . . . . . . . . . . . . . . . . . . . . . 2
DIAGNOSIS AND TESTING
SENTRY KEY IMMOBILIZER SYSTEM . . . . . . . . . 3
DESCRIPTION AND OPERATION
SENTRY KEY IMMOBILIZER SYSTEM
The Sentry Key Immobilizer System (SKIS) is
designed to provide passive protection against unau-
thorized vehicle use by preventing the engine from
operating. The primary components of this system
are the Sentry Key Immobilizer Module (SKIM), the
Sentry Key transponder, the SKIS indicator lamp,
and the Powertrain Control Module (PCM).
The SKIM is installed on the steering column near
the ignition lock cylinder. The transponder is located
under the molded rubber cap on the head of the igni-
tion key. The SKIS indicator lamp is located in the
instrument cluster.
The SKIS includes two valid Sentry Key transpon-
ders from the factory. If the customer wishes, addi-
tional non-coded blank Sentry Keys are available.
These blank keys can be cut to match a valid ignition
key, but the engine will not start unless the key tran-
sponder is also programmed to the vehicle. The SKIS
will recognize no more than eight valid Sentry Key
transponders at any one time.
The SKIS performs a self-test each time the igni-
tion switch is turned to the On position, and will
store Diagnostic Trouble Codes (DTCs) if a system
malfunction is detected. The SKIS can be diagnosed,
and any stored DTC can be retrieved using a DRB
scan tool as described in the proper Diagnostic Pro-
cedures manual.
SENTRY KEY IMMOBILIZER MODULE
The Sentry Key Immobilizer Module (SKIM) con-
tains a Radio Frequency (RF) transceiver and a cen-
tral processing unit, which includes the Sentry Key
Immobilizer System (SKIS) program logic. The SKIS
programming enables the SKIM to program and
retain in memory the codes of at least two, but no
2000 JEEP CHEROKEE
VEHICLE THEFT/SECURITY SYSTEMS
TABLE OF CONTENTS
page
SERVICE PROCEDURES
SENTRY KEY IMMOBILIZER SYSTEM
TRANSPONDER PROGRAMMING . . . . . . . . . . . 3
REMOVAL AND INSTALLATION
SENTRY KEY IMMOBILIZER MODULE. . . . . . . . . 4
more than eight electronically coded Sentry Key
transponders. The SKIS programming also enables
the SKIM to communicate over the Chrysler Collision
Detection (CCD) data bus network with the Power-
train Control Module (PCM), the instrument cluster
and/or the DRB scan tool.
The SKIM transmits and receives RF signals
through a tuned antenna enclosed within a molded
plastic ring formation that is integral to the SKIM
housing. When the SKIM is properly installed on the
steering column, the antenna ring is oriented around
the circumference of the ignition lock cylinder hous-
ing. This antenna ring must be located within eight
millimeters (0.31 inches) of the Sentry Key in order
to ensure proper RF communication between the
SKIM and the Sentry Key transponder.
For added system security, each SKIM is pro-
grammed with a unique "Secret Key" code and a
security code. The SKIM keeps the "Secret Key" code
in memory and sends the code over the CCD data
bus to the PCM, which also keeps this code in its
memory. The SKIM also sends the "Secret Key" code
to each of the programmed Sentry Key transponders.
The security code is used by the assembly plant to
access the SKIS for initialization, or by the dealer
technician to access the system for service. The
SKIM also stores in its memory the Vehicle Identifi-
cation Number (VIN), which it learns through a CCD
data bus message from the PCM during initializa-
tion.
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
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