Air Bag Systems: Description and Operation: Overview

THe Airbag Supplementary Restraint System (SRS) Is a safety device which, when used in conjunction with the seat belt, is designed to protect the driver and front passenger in the event of a frontal collision.




The diagnostic control unit (DCU) is able to distinguish between rough road conditions and a frontal collision. If the DCU detects a frontal collision of sufficient severity, it sends a fire signal to the airbag module initiators. The initiators ignite tablets of sodium azide which generate a large amount of Nitrogen gas leading to airbag inflation in approximately 30 milli-seconds.

As the occupant moves into the fully inflated airbag, the nitrogen gas discharges from vent holes in the rear of the airbag. As the airbag deflates, it provide progressive deceleration for the occupant and reduces the risk of injuries. The process from airbag initiation to deflation is completed in approximately 0.3 seconds.

WARNING: All the airbag system components, including the wiring harness, MUST be renewed after airbag deployment.

SRS Warning Lamps And System Diagnostics:

SRS warning light
The airbag system carries out a system check every time the ignition is switched to position 2. During the system check, the instrument pack warning light is illuminated to provide a bulb check. The warning lamp is extinguished when the system check is complete, after about 5 seconds.

If a system fault is found during the initial system check or subsequently during driving, the warning light will illuminate, indicating to the driver that there is a fault with the airbag system. With the warning light on, the airbag system will not operate in the event of a frontal collision. The DCU records system faults in an internal memory. The memory can be interrogated using TestBook via the diagnostic socket located on the passenger side fascia closing panel.