Jeep Cherokee 1999 Electronic Service Manual page 1275

14 - 32 FUEL SYSTEM—2.5L DIESEL ENGINE
DI AGN OSI S AN D T EST I N G (Cont inue d)
WARNING: THE GLOW
EXTREMELY HOT (GLOWING)
TESTS. BURNS COULD RESULT IF IMPROPERLY
HANDLED. ALLOW THE GLOW PLUG TO COOL
BEFORE REMOVING FROM TESTER.
(8) Rem ove t h e glow plu g fr om t h e t est er.
GLOW PLUG RELA Y TEST
Th e glow plu g r ela y is loca t ed in t h e en gin e com -
pa r t m en t on t h e left –in n er fen der (F ig. 17).
Fig. 17 Glow Plug Relay Location
Wh en t h e ign it ion (key) swit ch is pla ced in t h e ON
posit ion , a sign a l is sen t t o t h e E CM r ela t in g cu r r en t
en gin e coola n t t em per a t u r e. Th is sign a l is sen t fr om
t h e en gin e coola n t t em per a t u r e sen sor.
Aft er r eceivin g t h is sign a l, t h e E CM will det er m in e
if, wh en a n d for h ow lon g a per iod t h e glow plu g
r ela y sh ou ld be a ct iva t ed. Th is is don e befor e, du r in g
a n d a ft er t h e en gin e is st a r t ed. Wh en ever t h e glow
plu g r ela y is a ct iva t ed, it will con t r ol t h e 12V+ 100
a m p cir cu it for t h e oper a t ion of t h e fou r glow plu gs.
Th e Glow P lu g la m p is t ied t o t h is cir cu it . La m p
oper a t ion is a lso con t r olled by t h e E CM.
Wit h a cold en gin e, t h e glow plu g r ela y a n d glow
plu gs m a y be a ct iva t ed for a m a xim u m t im e of 200
secon ds. Refer t o t h e Glow P lu g Con t r ol ch a r t for a
t em per a t u r e/t im e com pa r ison of glow plu g r ela y oper-
a t ion .
In t h is ch a r t , P r e–H ea t a n d P ost –H ea t t im es a r e
m en t ion ed. P r e–h ea t is t h e a m ou n t of t im e t h e glow
plu g r ela y cir cu it is a ct iva t ed wh en t h e ign it ion (key)
swit ch is ON, bu t t h e en gin e h a s yet t o be st a r t ed.
P ost –h ea t is t h e a m ou n t of t im e t h e glow plu g r ela y
cir cu it is a ct iva t ed a ft er t h e en gin e is oper a t in g. Th e
Glow P lu g la m p will n ot be illu m in a t ed du r in g t h e
post –h ea t cycle.
PLUG WILL BECOME
DURING THESE
TES TIN G:
Discon n ect a n d isola t e t h e elect r ica l con n ect or s
(F ig. 18) a t a ll fou r glow plu gs. Wit h t h e en gin e cool
or cold, a n d t h e key in t h e ON posit ion , ch eck for
10–12 volt s + a t ea ch elect r ica l con n ect or. 10–12 volt s
+ sh ou ld be a t ea ch con n ect or wh en ever t h e E CM is
oper a t in g in t h e pr e–h ea t or post –h ea t cycles (r efer
t o t h e followin g Glow P lu g Con t r ol ch a r t ). B e v e ry
c a re fu l n o t to a llo w a n y o f th e fo u r d is c o n -
n e c te d g lo w p lu g e le c tric a l c o n n e c to rs to c o n -
ta c t a m e ta l s u rfa c e . Wh e n th e k e y is tu rn e d to
th e ON p o s itio n , a p p ro x im a te ly 100 a m p s a t 12
v o lts is s u p p lie d to th e s e c o n n e c to rs . If 10–12
volt s + is n ot a va ila ble a t ea ch con n ect or, ch eck con -
t in u it y of wir in g h a r n ess dir ect ly t o t h e r ela y. If con -
t in u it y is good dir ect ly t o t h e r ela y, t h e fa u lt is eit h er
wit h t h e r ela y or t h e r ela y in pu t fr om t h e E CM. To
t est t h e r ela y on ly, r efer t o Rela ys—Oper a t ion /Test -
in g in t h is sect ion of t h e gr ou p. If t h e r ela y t est is
good, r efer t o t h e DRB sca n t ool.
D ia g n o s tic Tro u ble Co d e s : Refer t o On -Boa r d
Dia gn ost ics in Gr ou p 25, E m ission Con t r ol Syst em
for a list of Dia gn ost ic Tr ou ble Codes (DTC's) for cer-
t a in fu el syst em com pon en t s.
Fig. 18 Wiring Connection at Glow Plug
RELA YS—OPERA TION/TESTING
Th e fo llo w in g d e s c rip tio n o f o p e ra tio n a n d
te s ts a p p ly o n ly to th e AS D a n d o th e r re la y s .
Th e t er m in a ls on t h e bot t om of ea ch r ela y a r e n u m -
ber ed (F ig. 19).
OPERA TION
• Ter m in a l n u m ber 30 is con n ect ed t o ba t t er y volt -
a ge. F or bot h t h e ASD a n d ot h er r ela ys, t er m in a l 30
is con n ect ed t o ba t t er y volt a ge a t a ll t im es.
• Th e E CM gr ou n ds t h e coil side of t h e r ela y
t h r ou gh t er m in a l n u m ber 85.
• Ter m in a l n u m ber 86 su pplies volt a ge t o t h e coil
side of t h e r ela y.
X J