Commu nication Interface (SCI) da ta bu s lin e for sup-
plemen tal restr ain t system program ming or dia gno-
sis and test ing th rough the 16-way Data Link
Connector (DLC) loca ted on the da sh pa nel below th e
dr iver side end of th e instrument panel. A hard wired
output from the ACM is u sed for cont rol of the airbag
indicator in th e Electr oMechanical Instrument Clus-
ter (EMIC). (Refer to 8 - E LECTRICAL/INSTRU-
MENT CLUSTER/AIRBAG INDICATOR -
OPERATION).
The ACM microprocessor cont inu ously monitors a ll
of t he supplement al rest raint system electr ical cir-
cuits t o deter mine the system readin ess. If th e ACM
detects a mon itored system fault, it set s an appropri-
ate Diagnostic Trou ble Code (DTC) an d sen ds an out-
pu t t o th e EMIC to t urn on the airba g indicator. The
ACM illumina tes th e in dicator for about fou r seconds
each t ime the ign ition switch is tur ned to the On
position as a bulb test . If the in dicator rema ins illu-
minated for about ten seconds a fter t he ign ition
switch is turned to the On position , the ACM ha s
detected a non-cr itical fau lt that poses no danger to
the vehicle occupant s. If t he a irba g indicator illumi-
nates solid (not flashing) while drivin g or stays on
longer tha n ten seconds following the bulb test, the
ACM has detect ed a cr itical fau lt t hat may cause t he
air bags n ot to deploy when requir ed or to deploy
when not requ ired. An active fault on ly remains for
the du ration of the fault, or in some cases, for th e
du ration of th e current ignition switch cycle, while a
st ored fa ult causes a DTC t o be stored in m emory by
the ACM.
The ACM receives battery curren t th rough a fused
ign ition switch output circuit. The ACM r eceives
ground th rough a ground circuit an d take out of the
vehicle wire harness. This ta ke ou t has an eyelet ter-
minal connector secured by a nut to a grou nd stud on
the floor panel dir ectly below the ACM within the
dr iver side seat r iser. A case groun d is also provided
for the ACM through a ground circuit and eyelet ter-
minal connect or secured under the left rea r ACM
mounting screw. Th ese con nections a llow the ACM t o
be opera tiona l wh enever th e ignit ion switch is in t he
On position.
The ACM also conta ins an ener gy-storage capa ci-
tor. When the ignition switch is in th e On posit ion,
this capacitor is cont inually being ch arged with
enough electrical energy t o deploy the supplemental
restraint com ponents for u p to one second following a
batt ery disconnect or fa ilure. The purpose of the
capacitor is to provide backup supplem enta l restrain t
system protection in case ther e is a loss of battery
curren t su pply to the ACM during an im pa ct.
Two sensor s ar e contained with in the ACM, an
electronic impa ct sensor and a safing sen sor. Th ese
electronic sen sor s are accelerometers that sense the
rate of vehicle decelerat ion, wh ich pr ovide verifica-
tion of the direction a nd severity of an impact. On
models equipped with opt iona l side curtain airbags,
the ACM also monitors input s from two remote side
impact sensors locat ed within the left and right front
door step wells to contr ol deployment of th e side cu r-
tain airbag units.
The sa fing sensor is an electr onic acceleromet er
sensor with in t he ACM t hat provides an a dditional
logic input to the ACM microprocessor. The safing
sensor is u sed to verify th e need for a supplemen tal
restraint deploymen t by detect ing impact energy of a
lesser magnitude than tha t of the primar y elect ronic
impact sen sor s, and m ust exceed a safing thr esh old
in order for th e airba gs to deploy. Vehicles equ ipped
with optional side curtain air bags fea ture a second
sa fing sensor within the ACM to provide confirma -
tion to th e ACM microprocessor of side impact forces.
This second safing sensor is a bi-directional unit that
detects impact for ces from eit her side of the vehicle.
Pre-program med decision a lgor ithms in the ACM
microprocessor determine wh en th e decelera tion rate
as signa led by the i m pa ct sen sor s an d th e safing sen-
sor s indica te a n impact that is severe enou gh to
require supplement al r est raint syst em pr otection.
When the progr amm ed condition s are met, t he ACM
sends the pr oper electrical signals to deploy the front
air bags and seat belt ten sioners and, if th e vehicle is
so equipped, eith er side cur tain air bag unit.
The ACM also provides a hard wired electrical
crash signal out pu t followin g a supplemen tal
restraint deployment even t. This output is used to
signal other electron ic modules in the vehicle to pro-
vide their en hanced accident response feat ures,
which in clude au tomatically disabling the en gine
from running and un locking all of th e doors. How-
ever, th ese responses are each dependen t upon the
circuits, com pon ents, a nd modules cont rolling these
featu res remainin g in tact fr om colla tera l damage
incurred dur ing the vehicle impact .
A single ACM is used for all variations of the sup-
plemen tal restra int system available in this vehicle.
This ACM is programmable and in order t o fu nction
pr operly it must be program med for the cor rect vehi-
cle supplement al rest raint system equipmen t using
an init ializa tion procedur e. Th e initia lization proce-
du re requires th e use of a diagnostic scan tool. Refer
to th e a ppr opr iate diagn ostic in formation. Th e h ard
wired inputs and outputs for the ACM may be diag-
nosed and t est ed using conventional diagn ost ic tools
and pr ocedures. H owever, conventional diagnostic
meth ods will not prove conclusive in t he diagn osis of
the ACM or th e su pplemental r est raint system. The
most r elia ble, efficient, a nd a ccurate means to dia g-
nose th e ACM or the su pplemen tal rest raint system
requires the use of a diagnostic scan tool. Refer to
the a ppr opr iate diagnostic informat ion.
VA RESTRAINTS 8O - 9
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