Air Bag Systems: Description and Operation

RESTRAINTS
Front Airbag System
A dual front airbag system is standard factory-installed safety equipment on this model. Both the driver and passenger airbag are certified to new federal regulations, which allows them to deploy with less force than prior airbags. The primary passenger restraints in this vehicle are the seat belts, which require active use by the vehicle occupants. The front airbag system is a supplemental passive restraint that was designed and is intended to enhance the protection for the front seat occupants of the vehicle when used in conjunction with the seat belts.

The driver airbag includes an inflatable airbag and an inflator unit behind a trim cover in the hub area of the steering wheel. The passenger airbag includes an inflatable airbag and an inflator unit behind an airbag door in the instrument panel above the glove box.

The dual front airbag system consists of the following components:
- Airbag Control Module (ACM)
- Airbag indicator lamp
- Clock Spring
- Driver and passenger airbags (including the airbag inflators)
- Wire harness and connections.

Refer to the proper Body Diagnostic Procedures to test or diagnose a problem with any component of the front airbag system.

The front airbag system electrical circuits are continuously monitored and controlled by a microprocessor and software contained within the Airbag Control Module (ACM). The ACM also contains an impact sensor and a safing sensor, which are monitored by the ACM to determine when an impact occurs that is severe enough to require front airbag system protection. When a frontal impact is severe enough, the ACM initiates the inflator units of both front airbag modules to deploy the airbags.

An airbag indicator lamp in the instrument cluster lights for about six to eight seconds as a bulb test each time the ignition switch is turned to the ON position. Following the bulb test, the airbag indicator lamp is turned ON or OFF by the ACM to indicate the status of the airbag system. If the airbag indicator lamp comes ON at any time other than during the bulb test, it indicates that there is a problem in the airbag system circuits. Such a problem may cause the airbags not to deploy when required, or to deploy when not required.

During a frontal vehicle impact, the knee blockers work in concert with properly adjusted seat belts to restrain the driver and front seat passenger in the proper position for an airbag deployment. The knee blockers also work to absorb and distribute the crash energy from the driver and front seat passenger to the structure of the instrument panel. The driver side knee blocker is integral to the left lower instrument panel bezel. The passenger side knee blocker is integral to the glove box door.

Following are general descriptions of the major components in the airbag system.

Side Impact Airbag System
Vehicles equipped with the Side Impact Airbag System utilize two airbags mounted to each front seat back frame. This system is designed to protect occupants in the event of a side impact collision.

The Side Impact Airbag Control Module (SIACM) controls the seat back mounted airbags. If the SIACM determines the impact is severe enough, the appropriate airbag/s will inflate, tearing open the front seat back trim cover/s protecting the passenger/s. Once a seat back mounted airbag has been deployed, all damaged parts must be replaced.

Fig.3 Airbag Control Module(ACM) Location:

AIRBAG CONTROL MODULE
The Airbag Control Module (ACM) contains the sensing element, safing sensor, and energy reserve capacitor. The module is mounted on the tunnel/floor pan between the gear shift lever and the park brake lever.

The ACM monitors the system to determine the system readiness. The ACM contains on-board diagnostics, and will illuminate the AIRBAG warning lamp in the cluster when a fault occurs. The warning equipment is tested for six to eight seconds every time the vehicle is started.

Fig.5 Child Tether Assembly:

Fig.6 Child Tether Anchor:

Fig.7 Child Tether Assembly Cap:

CHILD TETHER
The Child Tether Assembly consists of the Child Tether Anchor and the Child Tether Assembly Caps. The Child Tether Anchor is not serviceable. The anchor is located on the rear shelf panel. The Child Tether Assembly Cap is not serviceable. The rear trim panel will have to be replaced.

Fig.9 Clockspring Location:

CLOCKSPRING
The clock spring is mounted to the steering column behind the steering wheel. The clock spring is used to maintain a continuous electrical circuit between the wiring harness and the:
- Driver airbag module.
- Speed control switches.
- Horn switch.

The clockspring consists of a flat, ribbon like, electrically conductive tape which winds and unwinds with the steering wheel rotation.

Fig.11 Driver Airbag Location:

DRIVER AIRBAG
The driver airbag protective trim cover is the most visible part of the driver airbag system. The driver airbag is mounted directly to the steering wheel. Located under the airbag trim cover are the horn switch, the folded airbag cushion, and the airbag cushion supporting components. The resistive membrane-type horn switch is secured within a plastic tray between the driver airbag cover and the backer plate which is heat staked on to the driver airbag cover.

The driver airbag cannot be repaired, and must be replaced if deployed or in any way damaged. The driver airbag trim cover and the horn switch are available for service replacement.

The driver airbag includes a stamped metal housing to which the cushion and an inflator unit are attached and sealed. The conventional pyrotechnic-type inflator assembly is mounted to studs on the back of the airbag module housing. The inflator seals the hole in the airbag cushion so it can discharge the gas it produces directly into the cushion when supplied with the proper electrical signal. Following an airbag deployment, the airbag cushion quickly deflates by venting this gas towards the instrument panel through the porous fabric material used on the steering wheel side of the airbag cushion.

The protective trim cover is fitted to the front of the airbag and forms a decorative cover in the center of the steering wheel. The inside of the trim cover has locking blocks molded into it that engage a lip on the airbag metal housing. Two stamped metal retainers then fit over the inflator mounting studs on the back of the airbag 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 and tray unit upon airbag deployment.

Fig.14 Passenger Airbag Location:

PASSENGER AIRBAG
The passenger airbag is located behind the passenger airbag cover, between the glove box and instrument panel top cover.

The passenger airbag includes an aluminum housing within which the cushion and inflator are mounted and sealed. Two stamped metal brackets, one on each end of the housing, enclose the cushion and inflator. The mounting scheme consists of two weld studs and a bracket with two tabs off the bottom of the housing.

Following a passenger airbag deployment, the passenger airbag and the passenger airbag cover must be replaced. If inspection reveals that the passenger airbag mounting points on the instrument panel have been cracked or damaged, the instrument panel assembly must also be replaced. The passenger airbag cannot be repaired, and must be replaced if deployed or in any way damaged.

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 discharge the gas it produces directly into the cushion when supplied with the proper electrical signal. Following 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 passenger airbag is secured with nuts to the instrument panel beneath the instrument panel top pad and above the glove box opening.

Fig.17 Seat Airbag - Typical:

SEAT AIRBAG
The left and right seat airbags are located in the outboard edge of the front seat backs. The airbag contains a bag, an inflator (small canister of highly compressed gas), and a mounting bracket. The seat airbag cannot be repaired and must be replaced if deployed or in any way damaged.

When supplied with the proper electrical signal, the inflator seals the hole in the airbag cushion so it can discharge the compressed gas directly into the cushion. Upon deployment, the seat back trim cover will tear open and allow the seat airbag to fully deploy between the seat and the door.

Fig.23 Side Impact Airbag Control Module (SIACM):

SIDE IMPACT AIRBAG CONTROL MODULE
Vehicles equipped with side impact airbags use two side impact airbag control modules. One is located on each side of the vehicle within the body B-pillar.

Each side impact airbag control module (SIACM) serves as the impact sensor for its seat mounted airbag. The right side SIACM controls the right seat airbag. The left side SIACM controls the left seat airbag. Each SIACM contains two accelerometers, both accelerometers must agree in order to deploy the side airbag. In the event of a side impact, the appropriate SIACM will send a electronic signal to its airbag, deploying the airbag. The SIACM communicates with the Airbag Control Module (ACM) via the PCI bus circuit.

The SIACM perform self-diagnostics and circuit tests to determine if the system is functioning properly. If the test finds a problem, the SIACM will set both active and stored Diagnostic Trouble Codes (DTC's). If a DTC is active, the SIACM will request that the airbag warning lamp be turned on. The results of the system test are transmitted on the PCI bus circuit to the ACM once each second, or on a change in lamp state (ON/OFF). If the warning lamp status message from either SIACM contains a lamp ON request, the ACM will set an active DTC. At the same time as the DTC is set, the ACM sends a PCI bus message to the cluster requesting the airbag warning lamp to be turned ON. Observe all ACM WARNING and CAUTION statements when servicing or handling the SIACM. The SIACM's are not serviceable and must be replaced even if they are dropped.