Jeep Cherokee (XJ): Description and operation
The Sentry Key Immobilizer Module (SKIM) contains
a Radio Frequency (RF) transceiver and a central
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 one, but no
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 Powertrain
Control Module (PCM), the instrument cluster
and/or the DRBIIIt 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 housing.
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 programmed
with a unique "Secret Key" code and a
security code (PIN). The SKIM keeps the "Secret
Key" code in memory. This "Secret Key" code must be
transferred to the PCM memory during the initialization/
programming of the SKIS when the vehicle is
manufactured, and each time the PCM is replaced
during vehicle service by the dealer technician. The SKIM also transfers the
"Secret Key" code to the
memory of each of the Sentry Key transponders during
new key programming. 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 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 security
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 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 audible
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 DRBIIIt 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 The Sentry Key Immobilizer System (SKIS) uses a
transponder that is integral to each of the two ignition
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).
1 - MOLDED CAP Each Sentry Key transponder has a unique transponder
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 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 and their transponder identification
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 Programming
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 ignition switch is
turned to the Start or On positions, the SKIM transceiver
issues a Radio Frequency (RF) signal that excites
the transponder chip. The transponder chip responds by
issuing an RF signal containing its transponder identification
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. The Sentry Key Immobilizer System (SKIS) indicator
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 messages
received from the Sentry Key Immobilizer
Module (SKIM) on the Chrysler Collision Detection
(CCD) data bus.
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 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
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 audible
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.
The SKIS indicator lamp uses a replaceable incandescent
bulb and bulb holder on the instrument cluster
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 function,
diagnosis of the SKIS should be performed with
a DRB scan tool and the proper Diagnostic Procedures
manual.Sentry key immobilizer module
Sentry key immobilizer transponder
Fig. 1 Sentry Key Immobilizer Transponder
2 - TRANSPONDER
3 - MOLDED CAP REMOVED
4 - SENTRY KEYSentry key immobilizer system
indicator lamp
Other materials:
AW-4 automatic transmission
DESCRIPTION
The AW-4 is a 4-speed, electronically controlled
automatic transmission (Fig. 1).
The running gear consists of an oil pump, planetary
gear sets, clutch and brake units, hydraulic
accumulators, a valve body with electrical solenoids,
and a transmission control module (TCM). Cables ...