Chrysler Stratus RHD 1999 Electronic Service Manual page 463

8Q - 2 VEHICLE THEFT/SECURITY SYSTEMS
DESCRIPTION AND OPERATION (Continued)
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
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 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 igni-
tion 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 gen-
erate a single audible chime tone.
For diagnosis or initialization of the SKIM and the
PCM, a DRB 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).
Fig. 1 Sentry Key Immobilizer Transponder
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. When a Sentry Key
transponder is programmed into the memory of the
SKIM, the SKIM learns the transponder identifica-
tion code from the transponder, and the transponder
learns the "Secret Key" code from the SKIM. Each of
these codes is stored within the transponder and in
the nonvolatile memory of the SKIM. Therefore,
blank keys for the SKIS must be programmed by and
into the SKIM, 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.
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 igni-
tion switch is turned to the Start or On positions, the
SKIM transceiver issues a Radio Frequency (RF) sig-
nal that excites the transponder chip. The transpon-
der chip responds by issuing an RF signal containing
its transponder identification code and the "Secret
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