Jeep Cherokee 1999, Electronic Service Manual

Page: 458 / 1948

Th e swit ch es a lso h a ve LE D’s wh ich pr ovide ba ck-
ligh t in g wh en t h e ign it ion swit ch is in t h e ON posi-
t ion . Th e LE D’s ca n n ot be r epa ir ed. If t h e LE D is
fa u lt y, t h e in dividu a l swit ch m u st be r epla ced.
SEAT HEAT INTERFACE MODULE
Th e Sea t H ea t In t er fa ce Modu le (SH IM) is a n elec-
t r on ic m icr opr ocessor con t r olled device design ed t o
oper a t e t h e elect r ic sea t h ea t er elem en t s. Th e SH IM
is loca t ed u n der t h e r igh t fr on t sea t cu sh ion . In pu t s
t o t h e m odu le in clu de t h e con sole m ou n t ed r esist or
m u lt iplexed swit ch sign a ls, sea t cu sh ion t em per a t u r e
sen sor s, a r ela y-swit ch ed ba t t er y feed, a n d a gr ou n d.
Th e SH IM ou t pu t s a r e t h e feed for t h e sea t h ea t in g
elem en t s a n d sen sor s, a n d t h e swit ch t ellt a le cir cu it s.
Th e SH IM ca n n ot be r epa ir ed a n d, if fa u lt y or da m -
a ged, it m u st be r epla ced.
HEATED SEAT RELAY
Th e h ea t ed sea t r ela y is loca t ed u n der t h e r igh t
fr on t sea t cu sh ion n ea r t h e SH IM. Ign it ion a n d ba t -
t er y power is fed t o t h e r ela y, wh ich t h en pr ovides a
swit ch ed ba t t er y feed t o t h e SH IM. Th e h ea t ed sea t
r ela y ca n n ot be r epa ir ed a n d, if fa u lt y or da m a ged, it
m u st be r epla ced.
HEATED SEAT ELEMENT and SENSOR
Two h ea t ed sea t h ea t in g elem en t s a r e u sed in ea ch
fr on t sea t , on e for t h e sea t cu sh ion a n d t h e ot h er for
t h e sea t ba ck. Th e t wo elem en t s for ea ch sea t a r e
con n ect ed in ser ies wit h t h e SH IM.
Th e t em per a t u r e sen sor is a Nega t ive Tem per a t u r e
Coefficien t (NTC) t h er m ist or. On e t em per a t u r e sen -
sor is u sed for ea ch sea t , a n d it is in t egr a l t o t h e sea t
cu sh ion h ea t in g elem en t .
Th e h ea t in g elem en t s a r e sewn in t o t h e sea t cu sh ion
cover a n d sea t ba ck cover a ssem blies, wh ich a r e ser-
viced in dividu a lly. Th e h ea t in g elem en t s a n d t em per a -
t u r e sen sor ca n n ot be r epa ir ed a n d, if fa u lt y or
da m a ged, t h e a ffect ed sea t cover a ssem bly m u st be
r epla ced. Refer t o Gr ou p 23 - Body for t h e sea t cu sh ion
cover a n d sea t ba ck cover Rem ova l a n d In st a lla t ion .
DI AGN OSI S AN D T EST I N G
HEATED SEAT SYSTEM
F or cir cu it descr ipt ion s a n d dia gr a m s, r efer t o 8W -
63 - P ower Sea t Wit h H ea t ed Sea t s in Gr ou p 8W -
Wir in g Dia gr a m s.
WARNING: ON VEHICLES EQUIPPED WITH AIR-
BAGS,
REFER TO GROUP 8M - PASSIVE
RESTRAINT SYSTEMS BEFORE ATTEMPTING ANY
STEERING
WHEEL, STEERING COLUMN, OR
INSTRUMENT PANEL COMPONENT DIAGNOSIS OR
SERVICE. FAILURE TO TAKE THE PROPER PRE-
CAUTIONS COULD RESULT IN ACCIDENTAL AIR-
BAG DEPLOYMENT AND POSSIBLE PERSONAL
INJURY.
Th e h ea t ed sea t syst em is ca pa ble of per for m in g
som e self-dia gn ost ics. Th e followin g t a ble depict s t h e
va r iou s fa ilu r e m odes wh ich will be r epor t ed t o t h e
occu pa n t via fla sh in g t h e m om en t a r y swit ch t ellt a les.
Th e swit ch t ellt a les will fla sh on t h e dr iver ’s swit ch if
t h e fa ilu r e exist s in t h e dr iver ’s sea t por t ion of t h e sys-
t em , sim ila r ly wit h t h e pa ssen ger ’s swit ch . Th e t ellt a le
will illu m in a t e for a ppr oxim a t ely a
1 ⁄
2
secon d on , 1 ⁄
2
secon d off pu lse for a du r a t ion of on e m in u t e. Th is pr o-
cess will r epea t ever y t im e t h e syst em is in it ia t ed via
t h e swit ch es u n t il t h e pr oblem h a s been cor r ect ed.
SEAT H EAT I N T ERFACE M ODU LE DI AGN OST I C ROU T I N ES
FAILURE MODE SWITCH ! HI ! TELLTALE SWITCH ! LO ! TELLTALE
Shorted Heating Element Flashing Flashing
NTC Value Out of Range Off Flashing
Fig. 1 Heated Seat Switch Location
X J ELECTRICALLY HEATED SYSTEMS 8N - 9
DESCRI PT I ON AN D OPERAT I ON (Cont inue d)