Jeep Cherokee 1999 Electronic Service Manual page 1267

14 - 24 FUEL SYSTEM—2.5L DIESEL ENGINE
GEN ERAL I N FORM AT I ON (Cont inue d)
wh er e wit h in t h e fu el syst em . Th e DRBIII sca n t ool
is t h e best m et h od for com m u n ica t in g wit h t h e E CM
a n d P CM t o dia gn ose fa u lt s wit h in t h e syst em .
DESCRI PT I ON AN D OPERAT I ON
POWERTRAIN CONTROL MODULE (PCM)
On LH D veh icles, t h e E CM is m ou n t ed beh in d t h e
lower In st r u m en t P a n el t o t h e r igh t of t h e a cceler a -
t or peda l (F ig. 1). On RH D veh icles, t h e E CM is
m ou n t ed beh in d t h e lower In st r u m en t P a n el t o t h e
left of t h e clu t ch peda l. Th e P ower t r a in Con t r ol Mod-
u le (P CM) is m ou n t ed in t h e en gin e com pa r t m en t .
(F ig. 2).
Fig. 1 ECM Controller Location
Th e E CM Con t r oller is a pr e–pr ogr a m m ed, digit a l
com pu t er. It will eit h er dir ect ly oper a t e or pa r t ia lly
r egu la t e t h e:
• Speed Con t r ol
• Speed Con t r ol la m p
• F u el Tim in g Solen oid
• Ch eck E n gin e Ligh t
• Glow P lu g Rela y
• Glow P lu gs
• Glow P lu g La m p
• ASD Rela y
• Air Con dit ion in g
• Ta ch om et er
• E lect r ic Va cu u m Modu la t or (E VM)
Th e E CM ca n a da pt it s pr ogr a m m in g t o m eet
ch a n gin g oper a t in g con dit ion s.
Th e E CM r eceives in pu t sign a ls fr om va r iou s
swit ch es a n d sen sor s. Ba sed on t h ese in pu t s, t h e
E CM r egu la t es va r iou s en gin e a n d veh icle oper a t ion s
t h r ou gh differ en t syst em com pon en t s. Th ese com po-
n en t s a r e r efer r ed t o a s ECM Ou tp u ts . Th e sen sor s
Fig. 2 PCM Location
a n d swit ch es t h a t pr ovide in pu t s t o t h e E CM a r e
con sider ed ECM In p u ts .
ECM In p u ts a re :
• Air Con dit ion in g Select ion
• Th eft Ala r m
• ASD Rela y
• Con t r ol Sleeve P osit ion Sen sor
• F u el Tem per a t u r e Sen sor
• Ma ss Air F low Sen sor
• Acceler a t or P eda l P osit ion Sen sor
• E n gin e Coola n t Tem per a t u r e Sen sor
• Low Idle P osit ion Swit ch
• 5 Volt Su pply
• Veh icle Speed Sen sor
• E n gin e Speed/Cr a n k P osit ion Sen sor (r pm )
• Needle Movem en t Sen sor
• St a r t er Sign a l
• Br a ke Swit ch
• Speed Con t r ol Swit ch
• P ower Gr ou n d
• Ign it ion (key) Swit ch Sen se
ECM Ou tp u ts :
Aft er in pu t s a r e r eceived by t h e E CM a n d P CM,
cer t a in sen sor s, swit ch es a n d com pon en t s a r e con -
t r olled or r egu la t ed by t h e E CM a n d P CM. Th ese a r e
con sider ed ECM Ou tp u ts . Th ese ou t pu t s a r e for :
• A/C Clu t ch Rela y (for A/C clu t ch oper a t ion )
• Speed Con t r ol La m p
• ASD Rela y
• 5 Volt s Su pply
• F u el Qu a n t it y Act u a t or
• F u el Tim in g Solen oid
• F u el Sh u t down Solen oid
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