Description
Description
General
The Supplementary Restraint System (SRS) provides additional protection for front seat occupants during a frontal collision above a preset severity. The SRS is an electronically controlled, single point sensing system. The system comprises:
- An airbag Diagnostic Control Unit (DCU).
- A driver's airbag module.
- A front passenger's airbag module.
NOTE: In some markets an optional stowage bin is installed in place of the front passenger's airbag module.
- Two front seat belt pretensioners.
- A warning lamp.
Interconnecting wiring for the system is integrated into the vehicle harnesses. A rotary coupler connects the vehicle harness to the driver's airbag module. An ISO 9141 K line (bi-directional) serial communication link connects the airbag DCU to the vehicle's diagnostic socket.
The system is operational only while the ignition is on. With the ignition on, any frontal collision is detected by the airbag DCU. If the impact is above the preset severity, the DCU sends out simultaneous fire signals to the airbag modules and the seat belt pretensioners. The airbag modules then deploy protective airbags in front of the driver and front seat passenger, and the seat belt pretensioners retract to tighten the front seat belts. Collision detection to full deployment of the airbags and pretensioners takes approximately 45 milliseconds.
Airbag DCU
The airbag DCU controls the operation of the system and also contains the collision detection sensors. The airbag DCU is attached to a bracket on the transmission tunnel, directly below the heater. On pre 2002 MY vehicles, a vehicle earth connects to one of the fixings. A multi-pin connector provides the airbag DCU connection with the vehicle harness.
Incorporated into the airbag DCU is a mechanical safing sensor, an electronic single point sensor and integrated circuits for control and diagnostics. The mechanical safing sensor is a normally open switch that closes at the preset deceleration limit. The single point sensor is an accelerometer that produces an output proportional to the vehicle's deceleration.
Power Back-up
The airbag DCU incorporates capacitors to ensure the system will function if the external power supply is disconnected during a collision:
- Up to 2002 MY, the DCU incorporates a hardware capacitor, that provides power for 200 milliseconds to enable system operation and collision recording, and individual capacitors that provide power for 150 milliseconds for each fire signal output.
- From 2002 MY, the DCU incorporates individual capacitors that provide power for 150 milliseconds for each airbag fire signal output.
Airbag DCU Connector Pin Details (Up To 2002 MY)
Airbag DCU Connector Pin Details (From 2002 MY)
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. 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 60 litres (2.12 cu.ft); the passenger's airbag has an inflated volume of 150 litres (5.30 cu.ft). 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 DCU. 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.
Both airbag modules operate in the same way. On receipt of a fire signal from the airbag DCU, the igniter ignites the material in the gas generator. The burning material rapidly produces a large amount of nitrogen gas which passes through the filter screen into the airbag, forcing the airbag to unfold.
On the driver's airbag module, the unfolding airbag ruptures the cover along the split lines; on the passenger's airbag module, the unfolding airbag breaks the deployment door fixings to the module housing and trim panel, and the deployment door lifts off the fascia (but remains tethered to the module housing). Once free of the housing the airbag inflates to its full extent. Vents in the airbag prevent excess pressure bursting the bag and, as soon as the material in the gas generator is exhausted, allows the airbag to instantly deflate.
Seat Belt Pretensioners
During a frontal collision the seat belt pretensioners tighten the front seat belts to ensure the occupants are securely held in their seats. A pretensioner is integrated into the buckle assembly of each front seat belt.
The two pretensioners are handed, but otherwise identical. Each pretensioner has a tube containing propellant and a piston. The piston is attached to steel cables, the opposite ends of which are attached to the seat belt buckle. An igniter (squib) in the base of the tube provides an ignition source when triggered by a fire signal from the airbag DCU. A fly lead with a 2 pin connector links the igniter to the vehicle wiring.
On receipt of a fire signal from the airbag DCU, the igniter ignites the propellant. The burning propellant rapidly produces nitrogen gas that drives the piston along the tube, pulling on the cables and drawing the buckle towards the buckle assembly fixing point on the seat.
SRS Warning Lamp
The SRS warning lamp provides system status information for the driver. The lamp consists of a non serviceable LED behind a red SRS graphic, which is located below the speedometer in the instrument pack.
Rotary Coupler
The rotary coupler is installed on the steering column to provide the interface between the fixed wiring harness and the moveable driver's airbag module. In addition to the wiring for the driver's airbag module, the rotary coupler also provides the interface for the following switches which, depending on equipment level, can also be incorporated into the steering wheel:
- Horn switches.
- ICE system control switches.
- Cruise control system switches.
A rotating link harness is encapsulated into a plastic cassette comprising outer and inner housings with integral connectors. Screws attach the outer housing to the steering column switch assembly and the inner housing is keyed to the steering wheel by its connector.
The inner housing can turn a maximum of five revolutions in relation to the outer housing. For maintenance purposes the inner housing incorporates a position indicator wheel; a white segment is visible on the wheel when the rotary coupler is centralised. To prevent breaking the rotating link harness, both the steering and the rotary coupler must be centralised when removing and installing the steering wheel.
A new rotary coupler has a blue locking tab which ensures the unit is locked at its factory centred position. The peg should remain intact until just before steering wheel fitment.
