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 a steel cable, the opposite end of which is attached to the seat belt buckle. An igniter (squib) in the base of tube provides an ignition source when triggered by a fire signal from the airbag ECU. A fly lead with a 2 pin connector links the igniter to the vehicle wiring.

On receipt of a fire signal from the airbag ECU, the igniter ignites the propellant. The burning propellant rapidly produces nitrogen gas that drives the piston along the tube, pulling on the cable 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 bulb behind a red SRS graphic at the base of the tachometer in the instrument pack. The bulb is a serviceable item that can be renewed from the rear of the instrument pack.

Seat belt pretensioner components

1. Seat belt buckle
2. Gaiter
3. Steel cable
4. Fixing
5. Igniter
6. Fly lead
7. Vent
8. Tube