Contacteur de boucle de ceinture défectueux

The switch that tells the car whether a seat belt is fastened has failed, or its wiring has.

Most people know it as the thing that makes the chime stop, and that is its least important job. The restraints module uses belt state to decide how to deploy the airbag, because a belted and an unbelted occupant need opposite treatment. An unbelted person is already moving toward the dashboard when the bag fires, so it must inflate earlier and harder — while that same deployment into someone the belt is already restraining can do more harm than the crash would.

So a buckle switch reporting wrongly does not merely silence a chime; it makes the airbag deploy to the wrong plan. It is also what the pretensioner decision hangs on, since firing one on an unused belt spends a single-use device for nothing.

The commonest cause is not the switch. It is the wiring beneath the seat, which flexes on every adjustment and is routinely damaged by objects pushed underneath or by seats removed and refitted. Check the harness and connector before the buckle.

One benign cause worth eliminating first: coins, crumbs and debris in the buckle throat interfere with the switch mechanically. It is worth looking before anything is dismantled.