Jeep Cherokee 1999 Electronic Service Manual page 1234

X J
DI AGN OSI S AN D T EST I N G (Cont inue d)
Fig. 38 Intake Manifold Air Temperature Sensor—
2.5L Engine
du r in g per iods of h igh pu m p loa d a n d low en gin e
r pm ; su ch a s du r in g pa r kin g m a n eu ver s. Th e P CM
will t h en in cr ea se idle speed t h r ou gh t h e Idle Air
Con t r ol (IAC) m ot or. Th is is don e t o pr even t t h e
en gin e fr om st a llin g u n der t h e in cr ea sed loa d.
Wh en st eer in g pu m p pr essu r e exceeds 3275 kP a
690 kP a (475 psi
swit ch cir cu it will open a n d t h e P CM will in cr ea se
t h e en gin e idle speed.
Wh en power st eer in g pu m p pr essu r e dr ops t o
a ppr oxim a t ely 1379 kP a (200 psi), t h e swit ch cir cu it
will r e-close a n d idle speed will r et u r n t o n or m a l.
To te s t s w itc h :
(1) Discon n ect elect r ica l con n ect or a t swit ch .
(2) Con n ect a pa ir of ju m per wir es t o swit ch t er m i-
n a ls. Rou t e a n d secu r e ju m per wir es a wa y fr om fa n
bla des a n d fa n belt .
(3) Con n ect a n oh m m et er t o ju m per wir es a n d
obser ve con t in u it y. Cir cu it sh ou ld be closed wit h
en gin e n ot r u n n in g. If con t in u it y is obser ved, swit ch
is OK. If swit ch cir cu it is open , r epla ce swit ch .
(4) St a r t en gin e a n d obser ve oh m m et er. Wit h
en gin e a t idle speed, con t in u it y sh ou ld be obser ved
u n t il st eer in g wh eel h a s been t u r n ed t o left or r igh t
posit ion . D o n o t h o ld s te e rin g w h e e l in fu ll le ft
o r rig h t p o s itio n fo r m o re th a n a fe w s e c o n d s .
D a m a g e to p o w e r s te e rin g p u m p m a y o c c u r.
(5) If con t in u it y is st ill obser ved a ft er t u r n in g
wh eel (cir cu it did n ot open ) , r epla ce swit ch .
VEHICLE SPEED SENSOR
To per for m a com plet e t est of t h e sen sor a n d it s
cir cu it r y, r efer t o DRB sca n t ool a n d a ppr opr ia t e
P ower t r a in Dia gn ost ics P r ocedu r es m a n u a l.
100 psi), t h e n or m a lly closed
Fig. 39 Power Steering Pump Pressure Switch—2.5L
EXTENDED IDLE SWITCH TEST
OPTIONAL POLICE PACKAGE ONL Y
Th e ext en ded idle swit ch is u sed t o r a ise en gin e
idle speed t o a ppr oxim a t ely 1000 r pm wh en t h e
sh ift er is in eit h er P a r k or Neu t r a l posit ion . A r ocker-
t ype swit ch (ext en ded idle swit ch ) is m ou n t ed t o
in st r u m en t pa n el. Th is s w itc h is a v a ila ble o n ly
w ith 4.0L e n g in e w h e n s u p p lie d w ith o p tio n a l
p o lic e p a c k a g e .
Th e ext en ded idle swit ch will con t r ol a gr ou n d cir-
cu it goin g t o t h e power t r a in con t r ol m odu le (P CM).
Wh en a gr ou n d sign a l (t h r ou gh t h e swit ch ) h a s been
r eceived a t pin /ca vit y A-12 (cir cu it K78) of t h e P CM,
en gin e idle speed will in cr ea se.
(1) Br in g en gin e t o n or m a l oper a t in g t em per a t u r e
a n d t u r n ext en ded idle swit ch t o ON posit ion . E n gin e
idle speed sh ou ld n ow in cr ea se t o a ppr oxim a t ely
1000 r pm wh en sh ift er is in eit h er P a r k or Neu t r a l
posit ion .
(2) If idle speed does n ot in cr ea se, u n plu g 4–wa y
elect r ica l con n ect or fr om swit ch .
(3) Ch eck cir cu it Z1L for gr ou n d. Gr ou n d sh ou ld
be pr esen t a t a ll t im es. If n ot , r epa ir open cir cu it t o
gr ou n d. Refer t o Gr ou p 8W, Wir in g Dia gr a m s for cir-
cu it a n d wir in g in for m a t ion .
(4) If gr ou n d is pr esen t a t Z1L, ch eck con t in u it y of
swit ch bet ween cir cu it s Z1L a n d K78. If con t in u it y is
n ot pr esen t , r epla ce swit ch . If swit ch is OK pr oceed
t o n ext st ep.
(5) Wit h 4–wa y elect r ica l con n ect or st ill u n plu gged
fr om swit ch , a pply a good gr ou n d t o cir cu it K78.
E n gin e idle speed sh ou ld in cr ea se. If n ot , pr oceed t o
n ext st ep.
FUEL SYSTEM
Engine
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