System Description

System Description

The airbag system installation comprises:

• Airbag Diagnostic Module
• Driver and passenger airbag modules
• Two front impact (crash) sensors
• One 'safing' sensor
• Dedicated wiring harness
• SRS indicator/warning lamp

The system is designed to provide protection for both driver and front seat passenger by automatically deploying airbags in the event of a collision during forward travel.

In the event of a collision, the crash and safing sensors will operate, completing the firing circuit and causing the airbags to inflate within 32 milliseconds. At least one crash sensor and the safing sensor must operate to fire the airbags.

Any faults in system components, installation or wiring will be indicated by a flashing code on the SRS/AIRBAG warning lamp. Fault code information may also be monitored using the PDU or scan tool.

Component Descriptions

Airbag Diagnostic Module

The airbag diagnostic module is mounted on top of the passenger airbag mounting cage. The diagnostic module contains the microprocessor which is connected to the complete airbag system. The state of the three system sensors, the two airbag modules and the wiring harness is constantly monitored by the microprocessor for faults and for sensor activation (crash) conditions.

The diagnostic module also confirms correct supply voltage by comparing a direct battery voltage input with a similar input via the ignition switch.

The diagnostic module contains a reserve power supply, enabling the airbags to fire even if the supply voltage is lost due to collision damage. The reserve power charge will be retained for approximately one minute if the positive battery supply is lost in a collision. An auxiliary internal circuit known as the 'dwell enhancer' provides a temporary ground if normal system ground was lost in a collision.

Wiring Harness

A dedicated electrical wiring harness is used to connect all system components to the bulkhead harness. To allow free movement of the steering mechanism, a cable reel cassette is used to connect the drivers airbag in the steering wheel to the airbag harness on the steering column.

Airbag Modules

The two airbag modules contain a charge of sodium azide/copper oxide which will generate a sufficient volume of nitrogen gas to fully inflate the airbag when ignited by an electrical impulse. The volume of gas is greater in the passenger side airbag due to its larger size.

Both airbag modules, including the surrounding trim of the drivers airbag, are non-serviceable and once deployed, must be renewed as a complete assembly.

Crash and Safing Sensors

The two crash sensors are mounted one at either side of the bumper mounting cross member, outside of the bonnet hinges.

The safing sensor is mounted in the base of the drivers side 'A' post.

The two crash sensors and the safing sensor determine when airbag deployment is necessary in a crash condition.

The sensor contacts will only close when the vehicle suffers a forward impact of sufficient force. At least one crash sensor and the safing sensor contacts must close before the airbags will deploy. The double trigger strategy is used to prevent deployment during trivial impacts such as contacts during parking.