Certain criteria must be met for a diagnostic
trouble code to be entered into the SKIM memeory.
The criteria may be a range of; Input voltage, CCD
Bus message, or coded messages to the SKIM. If all
of the criteria for monitoring a circuit or function
are met and a fault is sensed, a diagnostic trouble
code will be stored in the SKIM memory.
3.2.8 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 neergizes the antenna
(this activates the transponder chop 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 tranponders.
Challenge -This is a random numbr 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 the SKIM. After responding to the coded
message, the transponder sends a transponder ID
message to the SKIM. The SKIM compares the
transponder ID to the available valid key codes in
the SKIM memory (8 key maximum). After validat-
ing the key the SKIM sends a CCD Bus message
called a ``Seed Request'' to the engine controller
then waits for a PCM response. If the PCM does not
respond, the SKIM will send the seed request agian.
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 Identification 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 the SKIM. After sending the valid/
invalid key massage 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 is
stored.
The SKIS incorporates a warning lamp (``ALARM
SET'') located in the message center. The lamp
receives switched ignition voltage and is hardwired
to the body control module. The lamp is actuated
when the SKIM sends a CCD Bus message to thebody controller requesting the lamp on. The body
controller then provides the ground for the lamp.
The SKIM will request lamp operation for the
following:
- bulb checks 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 tranponder fault the light flashes at a rate of 1
Hz (once per second). If a fault is pesent the lamp
will emain on or flashing for the complete ignition
cycle. If a fault is stored in SKIM memory which
prevents the system form 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.
3.2.9 PROGRAMMING THE POWERTRAIN
CONTROL MODULE
Important Note:Before replacing the PCM for a
failed driver, control circuit or ground circuit, be
sure to check the related component/circuit integ-
rity for failures not detected due to a double fault in
the circuit. Most PCM driver/control circuit failures
are caused by internal failure to components (i.e.
12-volt pull-ups, drivers and ground sensors). These
failures are difficult to detect when a double fault
has occurred and only one DTC has set.
NOTE:IF THE PCM AND THE SKIM ARE
REPLACED AT THE SAME TIME, PROGRAM
THE VIN INTO THE PCM FIRST. ALL VEHICLE
KEYS WILL THEN NEED TO BE REPLACED
AND PROGRAMMED TO THE NEW SKIM.
The SKIS ``Secret Key'' is an ID code that is
unique to each SKIS. This code is programmed and
stored in the SKIM, engine controller and transpon-
der ship (ignition key). When replacing the PCM it
is necessary to program the secret key into the
PCM.
1. Turn the ignition on (transmission in park/
neutral).
2. Use the DRB and select ``THEFT ALARM'',
SKIM then MISCELLANEOUS''.
3. Select ``PCM REPLACED''.
4. Enter secured access mode by entering the vehi-
cle four-digit PIN.
6
GENERAL INFORMATION
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