Jeep Cherokee 1999 Electronic Service Manual page 1268

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DESCRI PT I ON AN D OPERAT I ON (Cont inue d)
• Glow P lu g La m p
• Ch eck E n gin e La m p ("On /Off" sign a l)
• E lect r ic Va cu u m Modu la t or (E VM)
• Glow P lu g Rela y
• Ta ch om et er
Th e P CM sen ds a n d r ecieves sign a ls t o a n d fr om
t h e E CM con t r oller. P CM in p u ts a re :
• P ower Gou n d
• 5 Volt s Su pply
• Veh icle Speed Sen sor
• Wa t er-In -F u el Sen sor
• Coola n t Tem per a t u r e Sen sor
• Low Coola n t Sen sor
• Sen sor Ret u r n
• F u el Level Sen sor
• Oil P r essu r e Sen sor
• Ta ch om et er Sign a l
• Glow P lu g La m p
• Ch eck E n gin e La m p ("On /Off" sign a l)
• Br a ke On /Off Swit ch
• Ba t t er y Volt a ge
• ASD Rela y
P CM Ou tp u ts :
• A/C On Sign a l
• Veh icle Th eft Ala r m "Ok t o Ru n " sign a l
• Body Con t r ol Modu le CCD Bu s (+)
• Body Con t r ol Modu le CCD Bu s (–)
• Sca n Tool Da t a Lin k Recieve
• Sca n Tool Da t a Lin k Tr a n sm it
• Low Coola n t La m p
• Gen er a t or Con t r ol
BOOST / PRESSURE SENSOR
Th e Boost P r essu r e Sen sor is m ou n t ed t o t h e t op of
t h e in t a ke m a n ifold (F ig. 3). It is a sen sor t h a t m ea -
su r es bot h m a n ifold va cu u m a n d t u r bo boost , a n d it
a lso con t a in s a n in t egr a t ed in t a ke a ir t em per a t u r e
sen sor. Th e Boost P r essu r e Sen sor t a kes t h e pla ce of
t h e Ma ss Air F low (MAF ). In t h e In t a ke Air Tem per-
a t u r e Sen sor com pon en t , t h er e is a cer a m ic elem en t
t h a t ch a n ges it s r esist a n ce ba sed on t em per a t u r e.
Th e cer a m ic elem en t is pa r t of a n elect r on ic cir cu it
con n ect ed t o t h e P CM, a n d h a s a volt a ge a pplied t o
it . Th e cer a m ic elem en t is exposed t o t h e a ir in side
t h e in t a ke. Th is a ir h a s a coolin g effect on t h e
cer a m ic elem en t , a n d it s r esist a n ce ch a n ges. Th is
ca u ses t h e volt a ge flowin g t h r ou gh t h e in t a ke a ir
t em per a t u r e cir cu it t o va r y. Th e volt a ge sign a l pr o-
du ced by t h e In t a ke Air Tem per a t u r e Sen sor ch a n ges
in ver sely t o t h e t em per a t u r e, a n d is m ea su r ed by t h e
P CM. As a gen er a l r u le, wh en t h e t em per a t u r e of t h e
a ir in t h e in t a ke is h igh , t h e volt a ge sign a l pr odu ced
by t h e In t a ke Air Tem per a t u r e Sen sor is low. Th e
com pon en t of t h e Boost P r essu r e Sen sor t h a t m ea -
su r es m a n ifold va cu u m a n d t u r bo boost pr odu ces a
volt a ge sign a l t h a t is pr opor t ion a l t o t h e pr essu r e in
FUEL SYSTEM—2.5L DIESEL ENGINE
t h e in t a ke m a n ifold. Wh en t h e in t a ke m a n ifold pr es-
su r e is low, t h e volt a ge is low, a n d wh en t h e pr essu r e
is h igh , t h e volt a ge is h igh . Th e P CM u ses t h e volt -
a ge sign a ls fr om t h e Boost P r essu r e Sen sor, a n d t h e
In t a ke Air Tem per a t u r e Sen sor t o det er m in e t h e
a m ou n t of a ir flowin g t h r ou gh t h e in t a ke m a n ifold.
Fig. 3 Boost Pressure Sensor Location
VEHICLE THEFT ALARM
Th e P CM ca n lea r n if t h e veh icle h a s a Veh icle
Th eft Ala r m (VTA) syst em . On ce it det ect s t h e veh i-
cle h a vin g VTA, th e c o n tro lle r c a n ON LY B E
U S ED ON VEHICLES WITH VTA.
If t h e P CM is pu t it on a veh icle wit h ou t VTA t h e
Glow P lu g La m p will st a r t t o blin k a n d t h e veh icle
will n ot st a r t .
Th e P CM ca n n ot be fla sh ed t o r em ove t h e VTA.
BA TTERY VOLTAGE—PCM INPUT
Th e ba t t er y volt a ge in pu t pr ovides power t o t h e
P CM. It a lso in for m s t h e P CM wh a t volt a ge level is
bein g su pplied by t h e gen er a t or on ce t h e veh icle is
r u n n in g.
Th e ba t t er y in pu t a lso pr ovides t h e volt a ge t h a t is
n eeded t o keep t h e P CM m em or y a live. Th e m em or y
st or es Dia gn ost ic Tr ou ble Code (DTC) m essa ges.
Tr ou ble codes will st ill be st or ed even if t h e ba t t a r y
volt a ge is lost .
SENSOR RETURN—ECM/PCM INPUT (ANALOG
GROUND)
Sen sor Ret u r n pr ovides a low n oise An a log gr ou n d
r efer en ce for a ll syst em sen sor s.
IGNITION CIRCUIT SENSE—MSA/PCM INPUT
Th e ign it ion cir cu it sen se in pu t sign a ls t h e MSA
a n d P CM t h a t t h e ign it ion (key) swit ch h a s been
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