SKREES. The secret key is stored in the SKREEM,
ECM and all ignition key transponders.
Challenge - This is a random number that is
generated by the SKREEM at each ignition key
cycle.
The secret key and challenge are the two vari-
ables used in the algorithm that produces the
encrypted response message. The transponder uses
the crypto algorithm to receive, decode and respond
to the message sent by the SKREEM. After re-
sponding to the coded message, the transponder
sends a transponder I.D. message to the SKREEM.
The SKREEM compares the transponder I.D. to the
available valid key codes in the SKREEM memory
(8 key maximum at any one time). After validating
the key ignition the SKREEM sends a PCI Bus
message called a Seed Request to the engine con-
troller then waits for a ECM response. If the ECM
does not respond, the SKREEM will send the seed
request again. After three failed attempts the
SKREEM will stop sending the seed request and
store a trouble code. If the ECM sends a seed
response, the SKREEM sends a valid/invalid key
message to the ECM. 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 ECM at each ignition key cycle.
The VIN and seed are the two variables used in
the rolling code algorithm that encrypts the valid/
invalid key message. The ECM uses the rolling code
algorithm to receive, decode and respond to the
valid/invalid key message sent by the SKREEM.
After sending the valid/invalid key message the
SKREEM waits 3.5 seconds for a ECM status
message from the ECM. If the ECM does not
respond with a valid key message to the SKREEM,
a fault is detected and a trouble code is stored.
The SKREES incorporates a VTSS LED located
on the instrument panel upper cover. The LED
receives switched ignition voltage and is hardwired
to the body control module. The LED is actuated
when the SKREEM sends a PCI Bus message to the
body controller requesting the LED on. The body
controller then provides the ground for the LED.
The SKREEM will request VTSS LED operation for
the following:
– bulb checks at ignition on
– to alert the vehicle operator to a SKIS mal-
function
– customer key programming mode
For all faults except transponder faults and VTSS
LED remains on steady. In the event of a transpon-
der fault the LED flashes at a rate of 1 Hz (once per
second). If a fault is present the LED will remain on
or flashing for the complete ignition cycle. If a fault
is stored in SKREEM memory which prevents the
system from operating properly, the ECM will allow
the engine to start and run (for 2 seconds) up to six
times. After the sixth attempt, the ECM disables
the starter relay until the fault is corrected.
3.3
DIAGNOSTIC TROUBLE CODES
Each diagnostic trouble code (DTC) is diagnosed
by following a specific procedure. The diagnostic
test procedure contains step-by-step instruction for
determining the cause of the DTC as well as no
trouble code problems. It is not necessary to per-
form all of the tests in this book to diagnose an
individual code.
Always begin diagnosis by reading the DTCs
using the DRBIII
t. This will direct you to the
specific test(s) that must be performed.
3.3.1
HARD CODE
A DTC that comes back within one cycle of the
ignition key is a hard code. This means that the
problem is current every time the ECM/SKREEM
checks that circuit or function. Procedures in this
manual verify if the DTC is a hard code at the
beginning of each test. When the fault is not a hard
code, an intermittent test must be performed.
NOTE: If the DRBIII
t displays faults for multiple
components (i.e. ECT, VSS, IAT sensors) identify
and check the shared circuits for possible problems
before continuing (i.e. sensor grounds or 5-volt
supply circuits). Refer to the appropriate schematic
to identify shared circuits.
3.3.2
INTERMITTENT CODE
A DTC that is not current every time the ECM/
SKREEM checks the circuit or function is an inter-
mittent code. Most intermittent DTCs are caused
by wiring or connector problems. Problems that
come and go like this are the most difficult to
diagnose; they must be looked for under specific
conditions that cause them. The following checks
may assist you in identifying a possible intermit-
tent problem.
•
Visually inspect the related wire harness connec-
tors. Look for broken, bent, pushed out, or cor-
roded terminals.
•
Visually inspect the related wire harness. Look
for chafed, pierced, or partially broken wire.
•
Refer to hotlines or technical service bulletins
that may apply.
NOTE: Electromagnetic (radio) interference can
cause an intermittent SKREES malfunction. This
interference can interrupt communication between
the ignition key transponder and the SKREEM.
3
GENERAL INFORMATION