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DEPLOYMENT • REMOVAL • CLEANUP • INSTALLATION
In a vehicle collision, airbags will deploy even if vehicle speeds are as low as 15 mph. After deployment, in addition to repairs to the vehicle, replacing the airbag assembly itself can be a labor-intensive process.
The Supplemental Restraint System (SRS) on any vehicle consists of two primary subsystems: active restraints and passive restraints. Active restraints are those which require the occupants to perform an action for the device to deploy; for example, a seat belt. A passive restraint requires no action on the part of the occupants to deploy; for example, an airbag.
The multi-stage passenger air bag (PAB) is deployed by electric signals generated by the Occupant Restraint Controller (ORC) through the two or three multiple PAB squib circuits to the multiple initiators in the airbag inflator. The use of multiple initiators allows the airbag to be deployed at multiple levels of force. This was not always the case. Early airbags were deployed with the same force on every deployment.
The horizontal surface of the instrument panel top pad ① above and forward of the upper glove box ② is the most visible part of the passenger airbag, the subject of this article (see Figure 1). A seamless PAB is located under the top of the instrument panel cover above the glove box.
The force level is controlled by the ORC to suit the monitored impact conditions (severity of the collision) by providing one of several delay intervals between the electrical signals provided by the multiple initiators. As the time delays between these signals, the airbag deploys less or more forcefully.
When the ORC sends the proper electrical signal to each initiator, the electrical energy generates enough heat to start a small pyrotechnic charge which produces the pressure required to rupture the containment disk in the inflator canister. The inflator canister is sealed in the airbag cushion. A diffuser in the inflator directs all the gas into the airbag cushion, causing the cushion to inflate. As the cushion inflates, the PAB door area in the instrument panel splits open allowing the airbag to fully inflate.
In most cases, most initiators are used when the airbag is deployed. It is possible, though, for only one initiator to be used due to an airbag system fault. As a result of the possibility of such an event occurring, it is always necessary to confirm that all initiators have been used. Failure to do so can result in the improper disposal of potentially live pyrotechnic materials. The ORC monitors the condition of the airbags through circuit resistance. If a fault is detected, the airbag indicator in the instrument panel illuminates and a Diagnostic Trouble Code (DTC) is stored.
AFTER AIRBAG DEPLOYMENT
After an airbag is deployed, it must be replaced and a general clean-up of the inside of the vehicle as well as collision repair to the exterior will be necessary. In addition to this repair work, check the following items:
It is critical that the mounting surfaces and mounting brackets for the ORC and the impact sensors located in the proximity of the impact damage be closely inspected. If damaged, these components must be restored to original condition.
When the passenger airbag (PAB) has been deployed, as in this case, the airbag, PAB wire harness or connector and the upper instrument panel cover must be replaced. The instrument panel, cross car beam and PAB mounting brackets must be inspected.
Before beginning any airbag service work, disconnect and isolate the battery negative (ground) cable, then wait two minutes for the system capacitor to discharge. This is the only way to disable the SRS.
Let’s get started with removing the deployed airbag. (See Figure 2). Remove the airbag and instrument panel cover ① as a unit from the instrument panel support structure. Place these components on a suitable work surface with the top of the cover facing down. Disengage each of the six hooks ③ of the airbag housing ② from the windows in the forward wall of the airbag retainer ④ on the underside of the cover. To disengage the hooks, use hand pressure to push the adjacent edge of the airbag housing firmly and evenly downward into the airbag retainer while at the same time pulling outward on that edge of the retainer wall.
With all the forward hooks disengaged, roll the forward edge of the airbag housing upward to disengage the five lower hooks. Next, lift the housing and cushion from the retainer on the underside of the instrument panel cover.
Following an airbag deployment, the interior of the vehicle may be covered with a powdery residue. Most of it consists of harmless particulate byproducts of the pyrotechnic charge for deploying the airbag. Some of the residue, though, might contain traces of sodium hydroxide which can irritate the skin, eyes, nose and throat. Always wear safety glasses, rubber gloves and a long-sleeved shirt during cleanup.
Use a vacuum cleaner to remove the residual powder from the interior of the vehicle. Clean from the outside and work your way inside to avoid kneeling or sitting in the residue. Be certain to vacuum the heater and air conditioning outlets (see Figure 3). Operate the heater and air conditioning blower on the lowest speed setting and vacuum any powder
blown out of the outlets.
NEW AIRBAG INSTALLATION
Once again, (see Figure 2). Before installing the new airbag in the vehicle, place the instrument panel cover ① on a suitable work surface with the receptacle of the airbag retainer ④ facing up. Take care to prevent cosmetic damage to the cover.
Carefully position the airbag housing ① into the airbag retainer with the cushion side facing the instrument panel cover. Working around the perimeter of the airbag, engage each of the 11 hooks ③ on the airbag housing through the windows in the rearward and forward walls of the airbag retainer. After the airbag has been assembled in the retainer, try pulling the instrument cover and airbag housing away from each other. These components should not pull apart. Verify that all of the hooks are engaged.
Reinstall the airbag assembly and instrument panel cover as a unit onto the instrument panel support structure. Install and tighten the screws (normally two but possibly three) that secure the airbag bracket to the bracket of the instrument panel structural support. Tighten the screws to the proper torque.
Before reconnecting the negative (ground) battery cable to the battery, plug the airbag into the IP body harness and perform the Supplemental Restraint System Verification Test (refer to the appropriate service information for the vehicle being serviced from verification test specifics). Use the proper scan tool to perform this test, which includes erasing all prior DTC’s. When finished, reconnect the negative (ground) battery cable to the battery.