Seat Belt Pretensioners (Restraint systems)

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.

Seat Belt Pretensioner Components

1 Seat belt buckle 2 Gaiter 3 Steel cables 4 Fixing

5 Igniter 6 Fly lead 7 Piston tube

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: l Horn switches. l ICE system control switches. l 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.