Air Bag Systems: Description and Operation

Airbag Diagnostic Unit (ADU):

Air Bag-Supplemental Restraint System (SRS)
The Air Bag-Supplemental Restraint System (SRS) is designed to supplement driver and passenger seat belts during front-end collisions, reducing the risk of serious injury or death. Two collision-sensitive sensors are located in the Air Bag Diagnostic Unit (ADU). When a frontal collision of sufficient force occurs, the senses it causing ignition in each of the air bags. The driver is protected by a Steering Wheel mounted Air Bag, and, a Knee Air Bag, located behind the driver's knee bolster, and also, the passenger is protected by a passenger air bag, located on instrument panel.

The Knee Air Bag works in conjunction with the driver's seat belt to maintain their correct position in relation to the Steering Wheel mounted Air Bag in the event of a frontal collision. By absorbing the impact of the legs, the Knee Air Bag reduces the "submarine" effect which typically occurs in a frontal collision. By minimizing this effect, the Knee Air Bag causes the upper body to contact a larger surface area of the Steering Wheel Air Bag and at an improved angle which dramatically reduces the force transferred to the head and chest areas during a front collision. Although smaller than the Steering Wheel mounted Air Bag, the Knee Air Bag is attached directly to the Knee Bolster Panel which remains intact to provide a wider and flatter surface which is much better suited for contacting the legs of the driver.


Circuit Operation
The air bag diagnostic unit receives its power from the AIR BAG fuse. Two collision sensitive sensors in the air bag diagnostic unit are in series with each other and with the battery and all three air bag modules. When both sensors close simultaneously, squibs in the three bag modules will be initiated. The air bag diagnostic unit also contains a back-up power supply and a self-diagnostic function.