3.2.6 SKREEM OPERATION
Wh en ign it ion power is su pplied t o t h e SKRE E M,
th e SKREE M per form s a n in t er n a l self-test . Aft er
th e self-t est is com plet e, t he SKREE M en ergizes
th e an ten n a (th is a ct iva tes t h e tra n spon der chip)
an d sen ds a ch allen ge t o t h e t ra n spon der chip. Th e
tr a nspon der ch ip respon ds to th e ch a llen ge by gen -
er a t in g a n en cr ypted r espon se messa ge.
After respon din g t o t h e coded m essa ge, th e tr a n-
spon der sen ds a tr a n spon der ID m essa ge t o t he
SKRE E M. Th e SKRE EM com pa res t h e tr a nspon-
der ID m essa ge t o th e a va ila ble va lid key codes in
SKRE E M memor y (8 key m axim um a t a n y on e
tim e). After va lida tin g t he ign it ion key t he
SKRE E M sen ds a CAN Bu s messa ge r equest to t h e
ECM, t h en wa it s for t h e E CM respon se. If t h e E CM
does not r espon d, t he SKRE EM will sen d t h e re-
qu est aga in . If th e E CM does n ot r espon d a ga in , t he
SKRE E M will st op sen din g t he requ est a nd st or e a
tr ou ble code in memor y. If t h e E CM sen ds a corr ect
respon se t o t he SKRE E M, t h e SKRE EM sen ds a
va lid/in va lid key messa ge t o t h e ECM. Th e ECM
will a llow or disa llow en gin e oper a tion ba sed on t h is
message.
Secret Key - an elect ron ica lly st or ed va lu e (iden -
tifica t ion n um ber ) t h a t is u niqu e to ea ch SKRE EM.
Th e secr et key is st ored in th e SKRE EM, ECM a nd
all ign it ion key tr an spon der s.
Ch a llen ge - a r a n dom n u mber t h a t is gen er a t ed by
th e SKREE M at ea ch ign it ion key cycle.
Th e secret key an d ch a llen ge a re t he t wo va ri-
ables used in th e a lgor it h m th a t pr odu ces t h e
en cr ypt ed r espon se messa ge. Th e t ra n spon der uses
th e cr ypt o algor it h m to receive, decode a n d respond
to t h e m essa ge sen t by t h e SKRE EM. Aft er r e-
spon din g t o th e coded m essa ge, t h e t ra n spon der
sends a t r an spon der ID messa ge t o t he SKRE E M.
3.3 DIAGNOSTIC TROUBLE CODES
Ea ch dia gn ost ic trou ble code (DTC) i s dia gn osed
by followin g a specific pr ocedu re. The dia gnost ic
test pr ocedu re cont a in s st ep-by-step in st r uct ion for
deter m in in g t h e ca u se of t he DTC a s well a s n o
tr ou ble code pr oblem s. It is n ot n ecessa ry t o per-
form a ll of t he t est s in t h is book to dia gn ose a n
in dividu al code.
Alwa ys begin dia gn osis by r ea ding t h e DTCs
using the DRBIII". Th is will dir ect you t o t he
specific test (s) th at m u st be perfor m ed.
3.3.1 H AR D COD E
A DTC t ha t com es ba ck wit hin on e cycle of t he
ign it ion key is a h ar d code. Th is m ea ns t h a t t he
pr oblem is cu rr en t ever y t im e t h e E CM/SKRE E M
checks t ha t cir cuit or funct ion . P r ocedu res in th is
ma n ua l verify if the DTC is a h ar d code a t th e
begin n in g of ea ch t est . Wh en t he fa u lt is not a ha r d
code, an in ter m it t en t t est m u st be per form ed.
NOTE: If the DRBIII! displays faults for
multiple components (i.e. ECT, MAF, 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 t h a t is n ot cu r r ent ever y t im e t h e ECM/
SKRE E M ch eck s t he cir cu it or fu n ction is an in t er-
mit ten t code. Most in t erm it t ent DTCs a r e ca u sed
by wir in g or con n ect or pr oblem s. Pr oblem s t h at
come a n d go like th is a re th e m ost difficu lt to
dia gn ose; th ey m ust be looked for u nder specific
condit ion s t ha t cau se t h em . Th e followin g ch ecks
ma y a ssist you in iden t ifying a possible int er mit -
ten t pr oblem .
– Visu a lly inspect t h e rela ted wir e ha r n ess con -
nect or s. Look for br oken , ben t, push ed ou t or
corr oded t er m in a ls.
– Visu a lly in spect th e rela ted wir e h ar n ess.
Look for ch afed, pier ced or pa r tia lly br oken
wir e.
– Refer t o h otlin es or t echn ica l service bu llet in s
that may apply.
NOTE: Electromagnetic (radio) interference
can cause an intermittent system
malfunction. This interference can interrupt
communication between the ignition key
transponder and the SKREEM.
3.3.3 ECM DIAGNOSTIC TROUBLE CODES
IMPORTANT NOTE: Before replacing the
ECM for a failed driver, control circuit or
ground circuit, be sure to check the related
component/circuit integrity for failures not
detected due to a double fault in the circuit.
Most ECM driver/control circuit failures are
caused by internal failures to components
(i.e. relays and solenoids) and shorted
circuits (i.e. sensor pull-ups, drivers and
ground circuits). These faults are difficult to
detect when a double fault has occurred and
only one DTC has set.
If th e DRBIII" displa ys fau lt s for mu lt iple com-
pon en t s (i.e. MAF, ECT, E NG OIL, et c.), iden tify
an d check th e sh a r ed cir cuit s for possible pr oblem s
befor e con t in u in g (i.e. sen sor grou n ds or 5-volt
3
GEN ERAL I N FORM AT I ON
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