indicator LED, 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 VTSS indicator LED is located in the
instrument panel top cover.
OPERATION
The SKIS includes two valid Sentry Key transpon-
ders from the factory. These two Sentry Keys can be
used to program additional non-coded blank Sentry
Keys. These blank keys can be cut to match a valid
ignition key, but the engine will not start unless the
key transponder 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 (DTC’s) if a system
malfunction is detected. The SKIS can be diagnosed,
and any stored DTC can be retrieved using a DRB
IIIt scan tool as described in the proper Body Diag-
nostic Procedures Manual.
SENTRY KEY IMMOBILIZER MODULE (SKIM)
DESCRIPTION
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
more than eight electronically coded Sentry Key
transponders. The SKIS programming also enables
the SKIM to communicate over the Programmable
Communication Interface (PCI) bus network with the
Powertrain Control Module (PCM), and/or the DRB
IIIt scan tool.
OPERATION
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 (Fig. 1). 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 PCI 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 secu-
rity 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 Identification Number
(VIN), which it learns through a PCI 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.
Fig. 1 Sentry Key Immobilizer Module Location
1 – STEERING WHEEL
2 – IGNITION KEY CYLINDER
3 – STEERING COLUMN
4 – SENTRY KEY IMMOBILIZER MODULE
Fig. 2 Sentry Key Immobilizer Module
8Q - 2 VEHICLE THEFT/SECURITY SYSTEMS LH
DESCRIPTION AND OPERATION (Continued)
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