Chrysler PT Cruiser 2001 Service Manual Supplement page 2466

GENERAL INFORMATION
Certain criteria must be met for a diagnostic
trouble code to be entered into the SKIM memory.
The criteria may be a range of; Input voltage, PCI
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 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.
Challenger - 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 ID mes-
sage to the SKIM. The SKIM compares the tran-
sponder ID 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 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 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 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 red warning lamp lo-
cated in the instrument cluster. The lamp is actu-
ated when the SKIM sends a PCI Bus message to
the instrument cluster requesting the lamp on. The
SKIM will request lamp operation for the following:
− bulb checks at ignition on
− to alert the vehicle operator to a SKIS mal-
function
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.
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.
relay and solenoids) and short circuits (i.e. 12-volt
pull-ups, drivers and ground sensors). These fail-
ures 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, PCM and transponder chip (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.
NOTE: If three attempts are made to enter the
secure access mode using an incorrect PIN, secured
access mode will be locked out for one hour. To exit
this lockout mode, turn the ignition to the RUN
position for one hour then enter the correct PIN.
(Ensure all accessories are turned off. Also, monitor
the battery state and connect a battery charger if
necessary).
5. Press ENTER to transfer the secret key (the
SKIM will send the secret key to the PCM).
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