Seat Belt Tensioner: Description and Operation

Seat Belt Pre-Tensioners

Inertia reel three point seat belts are installed at each seat position, front and rear. The inertia reels are of the ALR (Automatic Locking Retractor) type. The MRS control unit at a slightly lower threshold level than the front airbags activates the front seat belt pre-tensioners.

The two pre-tensioners are side specific, but otherwise identical. Each pre-tensioner 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 the tube provides an ignition source when triggered by a fire signal from the MRS control unit. A fly lead with a 2-pin connector links the igniter to the vehicle's MRS wiring and is located on a bracket underneath the seat frame.