Sentry Key Immobilizer System Transponder Description And Operation - Jeep 200 Cherokee Service Manual

8Q - 2 VEHICLE THEFT/SECURITY SYSTEMS
DESCRIPTION AND OPERATION (Continued)
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 or transponder
fault when the ignition switch is turned to the On
position, it sends messages to the instrument cluster
to flash the SKIS indicator lamp.
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).
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
2000 JEEP CHEROKEE
Fig. 1 Sentry Key Immobilizer Transponder
1 – MOLDED CAP
2 – TRANSPONDER
3 – MOLDED CAP REMOVED
4 – SENTRY KEY
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
Key" code. The SKIM transceiver compares the tran-
sponder 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.
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