Air Bag Control Module: Description and Operation

The air bag control module, located under the floor console, governs the operation of the whole system and performs continual system diagnostics. Information on the severity of an impact is received from the crash sensor and, in the event of a side impact, the corresponding side impact sensor.

In the event of a frontal impact, in excess of a predetermined limit, the air bag control module will evaluate the signal received from the crash sensor and deploy the front air bag modules, driver safety belt retractor pretensioner and the front passenger safety belt buckle pretensioner dependent on the detected crash severity. However, the safety belt buckle pretensioners will only deploy if the safety belt buckle is fastened.

In the event of a side impact, in excess of a predetermined limit, the air bag control module will evaluate the signal received from the side impact sensors and deploy the corresponding side air bag module dependent on the detected crash type.

In the event of a failure in the vehicle power supply during an accident the air bag control module provides an auxiliary power supply sufficient to deploy the air bag(s) for a minimum of 150 mS. The vehicle battery supply maintains the air bag control module auxiliary supply and supports all other SRS functions when the ignition is in the 'RUN' position. In the event of a fault being detected by the air bag control module the air bag warning indicator is illuminated. The behavior of the warning indicator depends on the type of fault present.

Front Two Stage Air Bag Modules:

A new air bag control module must be installed following a collision in which the safety belt pretensioners or air bag(s) are deployed.

The driver air bag module is fitted to the steering wheel, the cover forming the outer surface of the steering wheel boss. The cover has invisible 'split lines' moulded in its surface allowing the air bag to easily exit through the cover when the system deploys.

A new driver air bag module and wiring harness with the air bag module electrical connectors must be installed following deployment.

The front passenger air bag module is located above the glove compartment and is secured to the cross-vehicle beam and the instrument panel. The front passenger air bag has a visible air bag door to allow the front passenger air bag to easily exit when the system deploys.

A new instrument panel, front passenger air bag module and wiring harness with the air bag module electrical connectors must be installed following deployment.

Both the driver and front passenger air bag modules contain two inflators.

In the event of a frontal impact, in excess of a predetermined limit, the air bag control module will deploy the driver air bag module first stage inflator. The second stage deployment is determined by the incident severity and the seat position sensor. From the evaluation of these conditions the second stage is either deployed between 10 mS and 30 mS or 100 mS following the first stage deployment.

The air bag control module will also deploy the front passenger air bag module first stage inflator. The second stage deployment is determined by the incident severity and occurs between 20 mS and 30 mS or 100 mS following the first stage deployment.

Deployment at 100 mS has negligible effect on the air bag inflation but is used as a "disposal" function to eliminate the risk of subsequent deployments.