an electronic impact sensor, and an energy storage
capacitor. The ACM housing has three integral
mounting tabs. A stamped metal cover plate is per-
manently secured to the bottom of the ACM housing
to enclose and protect the internal electronic circuitry
and components. An arrow printed on a label on the
top of the ACM housing near the rear provides a
visual verification of the proper orientation of the
unit, and should always be pointed toward the front
of the vehicle. A molded plastic electrical connector
receptacle containing numerous terminal pins is inte-
gral to the left facing side of the ACM housing. These
terminal pins connect the ACM to the vehicle electri-
cal system through a dedicated take out and connec-
tor of the vehicle wire harness.
The impact sensor internal to the ACM is cali-
brated for the specific vehicle, and is only serviced as
a unit with the ACM. The ACM cannot be repaired or
adjusted and, if damaged or faulty, it must be
replaced.
OPERATION
The microprocessor in the Airbag Control Module
(ACM) contains the supplemental restraint system
logic circuits and controls all of the supplemental
restraint system components. The ACM uses
On-Board Diagnostics (OBD) and can communicate
with the DRBIIIt scan tool using a diagnostic Serial
Communication Interface (SCI) data bus line for sup-
plemental restraint system programming or diagno-
sis and testing through the 16-way Data Link
Connector (DLC) located on the dash panel below the
driver side end of the instrument panel. A hard wired
output from the ACM is used for control of the airbag
indicator in the ElectroMechanical Instrument Clus-
ter (EMIC). (Refer to 8 - ELECTRICAL/INSTRU-
MENT CLUSTER/AIRBAG INDICATOR -
OPERATION).
The ACM microprocessor continuously monitors all
of the supplemental restraint system electrical cir-
cuits to determine the system readiness. If the ACM
detects a monitored system fault, it sets an appropri-
ate Diagnostic Trouble Code (DTC) and sends an out-
put to the EMIC to turn on the airbag indicator. The
ACM illuminates the indicator for about four seconds
each time the ignition switch is turned to the On
position as a bulb test. If the indicator remains illu-
minated for about ten seconds after the ignition
switch is turned to the On position, the ACM has
detected a non-critical fault that poses no danger to
the vehicle occupants. If the airbag indicator illumi-
nates solid (not flashing) while driving or stays on
longer than ten seconds following the bulb test, the
ACM has detected a critical fault that may cause the
airbags not to deploy when required or to deploy
when not required. An active fault only remains for
the duration of the fault, or in some cases, for the
duration of the current ignition switch cycle, while a
stored fault causes a DTC to be stored in memory by
the ACM.
The ACM receives battery current through a fused
ignition switch output circuit. The ACM receives
ground through a ground circuit and take out of the
vehicle wire harness. This take out has an eyelet ter-
minal connector secured by a nut to a ground stud on
the floor panel directly below the ACM within the
driver side seat riser. A case ground is also provided
for the ACM through a ground circuit and eyelet ter-
minal connector secured under the left rear ACM
mounting screw. These connections allow the ACM to
be operational whenever the ignition switch is in the
On position. The ACM also contains an energy-stor-
age capacitor. When the ignition switch is in the On
position, this capacitor is continually being charged
with enough electrical energy to deploy the supple-
mental restraint components for up to one second fol-
lowing a battery disconnect or failure. The purpose of
the capacitor is to provide backup supplemental
restraint system protection in case there is a loss of
battery current supply to the ACM during an impact.
An electronic impact sensor is contained within the
ACM. The electronic impact sensor is an accelerome-
ter that senses the rate of vehicle deceleration, which
provides verification of the direction and severity of
an impact. A pre-programmed decision algorithm in
the ACM microprocessor determines when the decel-
eration rate as signaled by the impact sensor indi-
cates an impact that is severe enough to require
supplemental restraint system protection. When the
programmed conditions are met, the ACM sends the
proper electrical signals to deploy the seat belt ten-
sioners and front airbags.
The ACM also provides a hard wired electrical
crash signal output following a supplemental
restraint deployment event. This output is used to
signal other electronic modules in the vehicle to pro-
vide their enhanced accident response features,
which include automatically disabling the engine
from running and unlocking all of the doors. How-
ever, these responses are each dependent upon the
circuits, components, and modules controlling these
features remaining intact from collateral damage
incurred during the vehicle impact.
A single ACM is used for all variations of the sup-
plemental restraint system available in this vehicle.
This ACM is programmable and in order to function
properly it must be programmed for the correct vehi-
cle supplemental restraint system equipment using
an initialization procedure. The initialization proce-
dure requires the use of a DRBIIIt scan tool. Refer to
the appropriate diagnostic information. The hard
wired inputs and outputs for the ACM may be diag-
VA RESTRAINTS 8O - 9
AIRBAG CONTROL MODULE (Continued)
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