Seat Belt Pretensioner

A pyrotechnic charge in the belt buckle or retractor that pulls several centimetres of slack out of the belt in the first milliseconds of a crash — before the airbag has begun to inflate — so that the occupant starts decelerating with the vehicle rather than after it. A load limiter then lets the webbing pay out at a controlled force. Some vehicles add a reversible motorised version that tightens under emergency braking and releases if no impact follows.

This is why the airbag is described as supplementary: the belt is the primary restraint, and the pretensioner is what makes it good enough to be one.

The module also reports buckle state, which matters more than it sounds: many vehicles change the airbag's deployment strategy according to whether the occupant is belted. A buckle contaminated with coins, crumbs and spilt drink can read as fastened when it is not — removing the reminder chime and misreporting the occupant. It is cleaned rather than replaced.

A fired pretensioner is replaced, never reset, and a belt worn in a collision should be replaced even if it looks perfect.

Also known as: pretensioner, belt pretensioner, seatbelt pretensioner, belt tensioner, seat belt tensioner, pyrotechnic buckle

Referenced by 55 codes

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Codes involving this component (55)

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