Functional Operation

FUNCTIONAL OPERATION
The airbag system is designed to provide increased driver and passenger protection if the vehicle is involved in a front-end collision. The system is most effective when used in conjunction with the seat belt system. The passenger side air bag assembly utilizes a canister of a compressed, inert gas to inflate the bag. This gas is expanded at a very high rate through a heating process. This allows a small quantity of gas under a very high pressure to inflate the large passenger airbag.

These vehicles utilize two front impact sensors and a safing sensor located in the Airbag System Diagnostic Module (ASDM) to control the deployment of the airbags. The ASDM is one type of Airbag Control Modules (ACM)

Diagnosis of the airbag system is done through the Data Link Connector (DLC) located under and just to the left of the steering column. The airbag lamp is located in the cluster. Whenever the ignition key is turned to the 'run" position, the cluster illuminates the bulb for 7 seconds. This illumination is called bulb prove-out. After the 7 seconds, the bulb will normally extinguish. The bulb will also illuminate if the ACM senses a fault in the Airbag system and communicates this fact to the cluster via the CCD bus. The cluster will also light the bulb if the ACM fails to communicate with it for 5 consecutive seconds. For most reasons the ACM commands the cluster to illuminate the airbag lamp and the ACM will keep the lamp illuminated for a minimum of 12 seconds. The AIRBAG warning lamp is the only point at which "symptoms" of a system malfunction can be observed by the customer. This lamp can not be dimmed.

In the event that the cluster detects a failure in the airbag lamp circuit, the cluster will substitute the seat belt lamp as a backup. If the airbag lamp is bad the cluster will flash the seat belt lamp for 20 seconds after prove-out time. If the airbag lamp must be turned on because of an airbag fault, the seat belt lamp will be used instead, but will flash for 20 seconds and then remain on continuously until the fault is fixed.

The ACM monitors critical input and output circuits within the airbag system, making sure they are operating correctly. Some circuits are tested continuously; others are checked only under certain circumstances. The ACM provides diagnostic information about the airbag system to the technician through the DRB via the CCD bus.

The deceleration or G-force resulting from the impact of a front-end collision causes the safing sensor inside the ASDM to close. As soon as one of the front impact sensors, and the safing sensor are closed, an electrical charge is sent to the airbag module. This causes the inflator to be actuated, thus deploying the airbags. The total time from the closure of the sensors to deployment and deflation of the airbags is 1/10 of one second.

The ACM also contains an energy storage capacitor. This capacitor stores enough electrical energy to deploy the airbags for up to 300 milliseconds following a battery disconnect or failure, during an impact event. The purpose of this feature is to provide airbag deployment in a severe secondary impact if the initial impact has damaged or disconnected the battery, but was not severe enough to deploy the airbags.