Restraint systems (Airbag modules): Description and operation

Fault code retrieval and fault diagnosis of the SRS can only be done using Testbook. Additional SRS information that can be read using Testbook is the:

• Airbag ECU bar code.
• Evolution number of the hardware, software and diagnostic protocol.
• Status of the crash locked mode.
• Vehicle identification number (VIN) data.

Diagnostic checks performed by the airbag ECU include:

• Monitoring of the airbag and pretensioner circuits for open/short circuits.
• Internal errors.
• Supply voltage (limits are 8.6 to 19.0 V at power up, 6.0 to 19.0 V during drive cycle).

Airbag modules

During a frontal collision each airbag module deploys a gas filled bag to form a protective cushion between the front seat occupant and the steering wheel or fascia/windshield. The driver’s airbag module is attached to the centre of the steering wheel. Where fitted, the passenger’s airbag module is installed in the fascia, above the glovebox.

Each airbag module has a gas generator attached to a folded airbag installed in a housing. The driver’s airbag has an inflated volume of 45 litres; the passenger’s airbag has an inflated volume of 120 litres. The gas generator of the driver’s airbag module is filled with a nitrocellulose based material; the gas generator of the passenger’s airbag module is filled with a sodium azide based material. The outlet of the gas generators incorporates a filter screen to prevent solid combustion by-products entering the airbag during deployment. An igniter (squib) in each generator provides an ignition source when triggered by a fire signal from the airbag ECU. A 2 pin connector provides the interface between the igniter and the vehicle wiring.

On the driver’s airbag module, the housing is closed by a cover that forms the steering wheel centre pad; split lines are formed in the inner surface of the cover to direct the airbag through the required exit point during deployment. On the passenger’s airbag module, the housing is closed by a trim panel profiled to match the fascia; a tethered deployment door forms an integral part of the trim panel.