3.2.2 ECM OPERATING MODES
As inpu t sign a ls to t h e E CM cha nge, t h e ECM
adju st s it s r espon se to t he ou tput devices. F or
exa m ple, t h e E CM mu st ca lcu la te a differ en t fu el
qu a n tit y a n d fu el t im in g for engin e idle con dit ion
th a n it wou ld for a wide open t h rot t le con dit ion .
Th er e a re sever a l differ ent m odes of oper at ion th a t
deter m in e h ow t h e ECM respon ds t o t he va r iou s
inp ut s ignals .
Ignition Switch On (Engine Off)
Wh en th e ign ition is t ur n ed on th e ECM act iva t es
th e glow plu g r ela y for a t im e per iod t ha t is det er-
min ed by en gin e coola n t t emper a tu r e, in t ake a ir
tem per at u re an d ba tt er y volt age.
Engine Start-Up Mode
Th e E CM u ses t he int a ke a ir t em per at u r e sen sor,
en gin e tem per at u re sen sor a n d t he cr an ksh a ft po-
sit ion sen sor (en gin e speed) in pu t s t o det er m in e
fuel inject ion qu a nt it y.
Normal Driving Modes
En gin e idle, wa r m-u p, accelera t ion , deceler at ion
an d wide open t h rot t le modes a r e cont rolled ba sed
on a ll of t h e sen sor in pu t s t o t he E CM. Th e E CM
uses t h ese sen sor in pu t s to a dju st fu el qu an t it y a n d
fuel in ject or t im in g. EGR va lve con tr ol is per for m ed
usin g feedba ck fr om t h e oxygen sen sor. An oxygen
sensor is loca t ed in th e exh a u st m a nifold t o sa m ple
oxygen con t ent exit in g t h e en gin e cylinder s. Th e
ECM u ses th e O2 sen sor, a lon g wit h ot h er sen sor
in pu t s, to govern t h e a m ou nt of exh au st ga s r ecir-
cula tion t o redu ce HC (H ydr oCa r bon s) an d CO
(Ca r bon Mon oxide). E n gin e coola nt is rou t ed
th r ough t h e ba se of t h e E GR va lve to pr ovide
addit ion a l coolin g of t he exh a ust ga s, wh ich fu rt h er
helps t h e r educt ion s of em ission s. Th e E GR va lve
ha s a self-clea n in g fun ct ion . Wh en t he en gin e is
sh ut off, th e E GR va lve r ot a tes t wice t o r edu ce
car bon deposit s a t th e va lve sea t.
Overheat Production Mode
If t h e en gin e tem per at u r e is a bove 105°C (221°F )
an d veh icle speed is a bove 40 km /h (25 MP H) th e
ECM will lim it fu el qu a nt it y for en gin e prot ect ion .
Limp-In Mode
Th e E CM u t ilizes differ en t degr ees of en gin e
lim p-in . Th e E CM is a ble t o lim it en gin e r pm ,
en gin e power out pu t (t ur bo boost r edu ction ), act i-
va t e en gin e coolin g fan or a ll of t h ese fu n ction s
ba sed on t he type of fa u lt t h at is det ect ed. Cr it ica l
en gin e per for ma n ce fault s su ch as a cceler at or peda l
posit ion sen sor fa ult will r esu lt in a fixed idle speed
of a ppr oxim at ely 680 r pm rega rdless of act u a l peda l
posit ion . Ot her less crit ica l fa u lt s will r esu lt in
power r educt ion t h rou gh ou t t h e fu ll r a nge of dr iv-
in g con dit ions.
Overspeed Detection Mode
If th e E CM det ect s en gin e RP M th a t exceeds
5200 RP M, t he E CM will set a DTC in m em ory,
lim it en gin e RP M t o n o m ore th an 2500 RP M, a n d
illu m in a te th e MIL u nt il t h e DTC is clea r ed.
After-Run Mode
Th e E CM t r a nsfer s RAM in for ma t ion to ROM
an d per forms a n In pu t/Ou t pu t st a t e check.
3.2.3 MONITORED CIRCUITS
Th e E CM is a ble to m on it or a n d iden tify most
dr ivea bilit y r ela t ed tr ou ble con dit ion s. Some cir-
cuit s a r e dir ect ly m on it or ed th r ou gh E CM feedba ck
cir cu it r y. In addit ion , th e ECM mon it ors t he volt age
st at e of som e cir cuit s a n d compa r es t h ose st a t es
wit h expect ed va lu es. Ot h er syst ems ar e mon it or ed
in direct ly wh en the ECM con du ct s a r at ion alit y test
to ident ify pr oblem s.
Alt h ough m ost su bsyst em s of t h e en gin e con t rol
modu le ar e eit h er dir ect ly or in direct ly monit ored,
th er e m a y be occa sion s wh en dia gn ost ic t rou ble
codes ar e n ot imm edia t ely iden tified. F or a t rou ble
code t o set , a specific set of con dit ions m u st occur
an d u n less t hese condit ion s occu r, a DTC will n ot
set.
3.2.4 SKREEM OVERVIEW
Th e sen tr y key rem ot e en t ry modu le syst em
(SKRE E M) is design ed to pr even t una u th or ized
veh icle oper a tion . Th e syst em con sist s of a sent r y
key r em ote en t ry module (SKRE E M), ign it ion
key(s) equ ipped wit h a tr a nspon der ch ip a nd t h e
ECM. Wh en t h e ign it ion swit ch is tur n ed on , t he
SKRE E M in t err oga t es th e ign ition key. If t h e ign i-
tion key is Valid or In va lid, th e SKRE E M sen ds a
messa ge t o t h e E CM in dica tin g ign it ion key st at u s.
Upon receivin g th is m essa ge t h e E CM will t er m i-
na t e en gin e oper at ion or a llow t h e en gin e t o con -
tin ue to opera t e.
3.2.5 SKREEM ON-BOARD DIAGNOSTICS
Th e SKRE EM h a s been pr ogr a m med t o tr a nsm it
an d mon it or m a ny differ en t coded m essa ges a s well
as CAN Bu s m essa ges. Th is monit orin g is called
On -Boa rd Dia gn ost ics. Cer t ain cr it er ia m u st be met
for a DTC t o be en t ered i n to SKREE M m em ory. Th e
crit eria m a y be a r an ge of; in pu t volt a ge, CAN Bu s
messa ge or coded messa ges t o t h e SKRE E M. If a ll
th e cr it er ia for m onit or in g a cir cuit or funct ion ar e
met a n d a fa ult is detect ed, a DTC will be st or ed in
th e SKRE E M mem or y an d th e START E RROR in di-
cat or will be tu rn ed on in t h e in st r um en t clu st er.
2
GEN ERAL I N FORM AT I ON
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