Description And Operation; Impact Sensors; Airbag System - Dodge ram truck 3500 1996 Service Manual

8 1 - 2 PASSIVE RESTRAINT SYSTEMS „ _ B R
D E S C R I P T I O N A N D O P E R A T I O N
AIRBAG MOiULE
The airbag module protective cover is the most vis­
ible part of the system. The module is mounted
directly to the steering wheel. Under the airbag mod­
ule cover, the airbag cushion and its supporting com­
ponents are contained. The airbag module contains a
housing to which the cushion and inflator are
attached and sealed. The airbag module cannot be
repaired, and must be replaced i f deployed or in any
way damaged.
The inflator assembly is mounted to the back of
the module. The inflator seals the hole in the airbag
cushion so i t can discharge the gas i t produces
directly into the cushion when supplied with the
proper electrical signal. The protective cover is fitted
to the front of the airbag module and forms a deco­
rative cover in the center of the steering wheel. Upon
airbag deployment, this cover will split horizontally.
STORAGE
The airbag module must be stored in its original,
special container until used for service. Also, i t must
be stored in a clean, dry environment; away from
sources of extreme heat, sparks, and high electrical
energy. Always place or store the module on a surface
with the trim cover facing up to minimize movement
in case of accidental deployment.
IMPACT SENSORS
The impact sensors provide verification of the
direction and severity of the impact. Three sensors
are used. One is called a sating sensor. It is located
inside the Airbag Control Module (ACM), which is
mounted to a bracket under the instrument panel, on
the top of the floor pan transmission tunnel. The
other two sensors are mounted on the inner fender
extension panels behind the grille opening reinforce­
ment, on the left and right sides of the vehicle. The
sensors are calibrated for the specific vehicle, and
react to the severity and direction of the impact.
The impact sensors are threshold sensitive
switches that complete an electrical circuit when an
impact provides a sufficient deceleration force to
close the switch. The safing sensor is an accelerome-
ter that senses the rate of deceleration. The micro­
processor in the ACM monitors the sensor signals. A
pre-programmed decision algorithm in the micropro­
cessor determines when the deceleration rate indi­
cates an impact that is severe enough to require
airbag system protection.
The impact sensors are available for service
replacement. The safing sensor is only serviced as
part of the ACM.
CL0CISPRIN6
The clockspring is mounted on the steering column
behind the steering wheel. I t is used to maintain a
continuous electrical circuit between the wiring har­
ness and the driver's side airbag module. This assem­
bly consists of a flat, ribbon-like electrically
conductive tape that winds and unwinds with the
steering wheel rotation.
AIRBAG CONTROL MOiULE
The Airbag Control Module (ACM) contains the
safing sensor, and a microprocessor that monitors the
airbag system to determine its readiness. I t also
monitors the impact sensors to determine when the
proper conditions exist to provide the electrical signal
that deploys the airbag. The ACM contains On-Board
Diagnostics (OBD), and will light the airbag warning
lamp in the instrument cluster when a monitored
airbag system fault occurs.
The ACM also contains an energy-storage capaci­
tor. This capacitor stores enough electrical energy to
deploy the airbag for up to two minutes following a
battery disconnect or failure. The purpose of the
capacitor is to provide airbag system protection in a
severe secondary impact i f the initial impact has
damaged or disconnected the battery, but was not
severe enough to deploy the airbag.
D I A G N O S I S A N D T E S T I N G
AIRBAG SYSTEM
A DRB scan tool is required for diagnosis of the
airbag system. Refer to the Airbag System - Body
Diagnostic Procedures manual for more information.
(1) Disconnect and isolate the battery negative
cable. I f the airbag system is undeployed, wait two
minutes for the system capacitor to discharge before
further service.
(2) Connect the DRB scan tool to the 16-way data
link connector. The connector is located under the
lower left corner of the instrument panel behind the
steering column cover/knee blocker (Fig. 1).
( 3 ) From the right side of the vehicle (away from
the airbag module i n case of an accidental deploy­
ment), turn the ignition switch to the On position.
Exit the vehicle with the DRB. Use the latest version
of the proper DRB cartridge.
(4) After checking that nobody is inside the vehi­
cle, reconnect the battery negative cable.
(5) Using the DRB, read and record the active
Diagnostic Trouble Code (DTC) data.
(6) Read and record any stored DTC data.
(7) Refer to the Airbag System - Body Diagnostic
Procedures manual, i f any DTC is found in Step 5 or
Step 6.