Dodge 2000 DURANGO Service Manual page 427

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DESCRIPTION AND OPERATION (Continued)
trim cover has locking blocks molded into it that
engage a lip on the airbag module metal housing.
Two stamped metal retainers then fit over the infla-
tor mounting studs on the back of the airbag module
housing and are engaged in slots on the inside of the
cover, securely locking the trim cover into place. The
trim cover will split at predetermined breakout lines,
then fold back out of the way along with the horn
switch upon airbag deployment.
PASSENGER SIDE AIRBAG MODULE
DESCRIPTION
The passenger side airbag door on the instrument
panel above the glove box is the most visible part of
the passenger side airbag system. Located under the
airbag door are the passenger side airbag cushion
and the airbag cushion supporting components.
The passenger side airbag module includes an
extruded aluminum housing within which the cush-
ion and inflator are mounted and sealed. The airbag
housing extrusion also includes two flanges. The
flanges, one at the top and one at the bottom, serve
as the mounting brackets for the module. Two
stamped metal brackets, one on each end of the hous-
ing, enclose the cushion and inflator. The passenger
side airbag module upper bracket is secured beneath
the instrument panel top pad with rivets to a flange
and bracket on the passenger side airbag door. The
lower bracket is secured with screws to the instru-
ment panel structural duct.
Following a passenger side airbag deployment, the
passenger side airbag module and the instrument
panel assembly must be replaced. The passenger side
airbag module cannot be repaired, and must be
replaced if deployed or in any way damaged.
OPERATION
The hybrid-type inflator assembly includes a small
canister of highly compressed argon gas. The inflator
seals the hole in the airbag cushion so it can dis-
charge the gas it produces directly into the cushion
when supplied with the proper electrical signal. Fol-
lowing an airbag deployment, the airbag cushion
quickly deflates by venting this gas through the
porous fabric material used on each end panel of the
airbag cushion.
The molded plastic passenger side airbag door is
secured to the instrument panel top cover with riv-
ets. The airbag door has predetermined breakout
lines concealed beneath its decorative cover. Upon
airbag deployment, the airbag door will split at the
breakout lines and the door will pivot out of the way.
The passenger side airbag door is serviced only as a
unit with the instrument panel top cover.
PASSIVE RESTRAINT SYSTEMS
AIRBAG CONTROL MODULE
DESCRIPTION
The Airbag Control Module (ACM) is secured with
screws to a mount welded onto the floor panel trans-
mission tunnel behind the instrument panel center
support bracket in the passenger compartment of the
vehicle. The ACM contains an electronic microproces-
sor, an electronic impact sensor, an electromechanical
safing sensor, and an energy storage capacitor.
The ACM cannot be repaired or adjusted and, if
damaged or faulty, it must be replaced.
OPERATION
The microprocessor in the ACM contains the airbag
system logic. The airbag system logic includes
On-Board Diagnostics (OBD), and the ability to com-
municate with the instrument cluster circuitry over
the Chrysler Collision Detection (CCD) data bus to
control the airbag indicator lamp. The microprocessor
continuously monitors all of the airbag system elec-
trical circuits to determine the system readiness. If
the ACM detects a monitored system fault, it sends
messages to the instrument cluster over the CCD
data bus to turn on the airbag indicator lamp. Refer
to Instrument Cluster in the proper section of
Group 8E - Instrument Panel Systems for more infor-
mation on the airbag indicator lamp.
One electronic impact sensor is used in this airbag
system. The impact sensor is an accelerometer that
senses the rate of vehicle deceleration, which pro-
vides verification of the direction and severity of an
impact. The impact sensor is calibrated for the spe-
cific vehicle, and is only serviced as a unit with the
ACM. A pre-programmed decision algorithm in the
ACM microprocessor determines when the decelera-
tion rate as signaled by the impact sensor indicates
an impact that is severe enough to require airbag
system protection. When the programmed conditions
are met, the ACM sends an electrical signal to deploy
the airbags.
In addition to the electronic impact sensor, there is
an electromechanical sensor within the ACM called a
safing sensor. The safing sensor is a normally open
series switch located in the airbag deployment circuit
of the ACM. This sensor detects impact energy of a
lesser magnitude than the electronic impact sensor,
and must be closed in order for the airbags to deploy.
The ACM also contains an energy-storage capaci-
tor. This capacitor stores enough electrical energy to
deploy the airbags for up to one second following a
battery disconnect or failure during an impact. The
purpose of the capacitor is to provide airbag system
protection in a severe secondary impact, if the initial
impact has damaged or disconnected the battery, but
was not severe enough to deploy the airbags.
8M - 3