Join Date: Mar 2005
Location: Tiny Pebble, AR
3.2.8 SKIS OPERATION
When ignition power is supplied to the SKIM, the
SKIM performs an internal self-test. After the selftest
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 algorithm
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 validating
the key the SKIM sends a PCI 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 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
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’’ message.
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
The SKIS incorporates a warning lamp located on
the instrument panel upper cover. The lamp receives
switched ignition voltage and is hardwired to
the body control module. The lamp is actuated when
the SKIM sends a PCI Bus message to the body
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 malfunction
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 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 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
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