After the ignition has been turned off, the power
sunroof will remain operational for an additional 45
seconds. If the front doors are opened during this
time, the BCM will remove power from the sunroof.
3.14
SENTRY KEY IMMOBILIZER SYSTEM
(SKIS)
The Sentry Key Immobilizer System (SKIS) is an
immobilizer system designed to prevent unautho-
rized vehicle operation. The system consists of a
Sentry Key Immobilizer Module (SKIM), ignition
key(s) equipped with a transponder chip and engine
controller. When the ignition switch is turned on,
the SKIM interrogates the ignition key. If the igni-
tion key is “Valid” the SKIM sends a PCI Bus
message to the engine controller indicating the
presence of a valid ignition key. Upon receiving a
“Valid” key signal the PCM will allow the engine to
continue to operate.
3.14.1
SKIS OPERATION
When ignition power is supplied to the SKIM, the
SKIM performs an internal self-test. After the self-
test is completed, the SKIM energizes the antenna
(this activates the transponder chip) and sends a
challenge to the transponder chip. The transponder
chip responds to the challenge by generating an
encrypted response message using the following:
Secret Key − This is an electronically stored value
(identification number) that is unique to each SKIS.
The secret key is stored in the SKIM, PCM and all
ignition key transponders.
Challenge − This is a random number that is
generated by the SKIM at each ignition key cycle.
The secret key and challenge are plugged into an
algorithm that produces the encrypted response
message. The transponder uses the crypto algo-
rithm to receive, decode and respond to the message
sent by SKIM. After responding to the coded mes-
sage, the transponder sends a transponder I.D.
message to the SKIM. The SKIM compares the
transponder I.D. to the available valid key codes in
SKIM memory (8 key maximum). After validating
the key the SKIM sends a PCI Bus message called
a “Seed Request” to the PCM then waits for a
controller response. If the PCM does not respond,
the SKIM will send the seed request again. After
three failed attempts the SKIM will stop sending
the seed request and store a trouble code. If the
PCM sends a seed response, the SKIM sends a
valid/invalid key message to the PCM. This is an
encrypted message that is generated using the
following:
VIN − Vehicle Indentification Number
Seed − This is a random number that is generated
by the PCM at each ignition key cycle.
The VIN and seed are plugged into a rolling code
algorithm that encrypts the “valid/invalid key” mes-
sage. The PCM uses the rolling code algorithm to
receive, decode and respond to the valid/invalid key
message sent by SKIM. After sending the valid/
invalid key message the SKIM waits 3.5 seconds for
a PCM status message from the PCM. If the PCM
does not respond with a valid key message to the
SKIM, a fault is detected and a trouble code stored.
The SKIS incorporates a warning lamp located in
the instrument cluster. The lamp is actuated when
the SKIM sends a PCI Bus message to the instru-
ment cluster requesting the lamp on. The SKIM
will request lamp operation for the following:
- bulb check at ignition on
- to alert the vehicle operator to a SKIS malfunc-
tion
For all faults except transponder faults and VIN
mismatch, the lamp remains on steady. In the event
of a transponder fault the light flashes at the rate of
1 Hz (once per second). If a fault is present the lamp
will remain on or flashing for the complete ignition
cycle. If a fault is stored in SKIM memory which
prevents the system from operating properly, the
PCM will allow the engine to start and run (for 2
seconds) up to six times. After the sixth attempt, the
PCM disables the starter relay until the fault is
corrected.
For additional information on the SKIS, refer to
the appropriate Powertrain Diagnostic Informa-
tion.
3.15
COMMUNICATION
The Programmable Communication Interface or
PCI Bus is a single wire multiplexed network capa-
ble of supporting binary encoded messages shared
between multiple modules. The PCI bus circuit is
identified as D25 and is yellow with a violet tracer.
Additional tracer colors may be added to the violet
in order to distinguish between different module
connections. The modules are wired in parallel.
Connections are made in the harness using splices.
One splice called the Diagnostic Junction Port,
serves as the “Hub” of the bus. The Diagnostic
Junction Port provides an access point to isolate
most of the modules on the bus in order to assist in
diagnosing the circuit. The following modules are
used on the WG:
•
Body Control Module
•
Door Modules (Driver & Passenger)
•
Airbag Control Module
•
Controller Antilock Brake
•
Powertrain Control Module
•
Radio
•
CD Changer
15
GENERAL INFORMATION