Capteur de choc dérangé lors d'une réparation de carrosserie

A crash sensor was removed, refitted or replaced during panel work, and something about how it went back is wrong.

This is the leading cause of restraints faults on any vehicle that has ever been repaired, and the reason is simply where the sensors live. They bolt to the bumper beam, the front rails, the B-pillars, the sills and the door structures — the exact parts removed for a bumper change, a headlight, a radiator, a door skin or a wing. None of that work is about airbags, so the sensors get treated as fasteners to undo rather than as calibrated instruments.

Four specific things go wrong, and each defeats a static test.

• Orientation. A sensor measures acceleration along a defined axis. Fitted rotated or reversed, it reads a genuine impact wrongly while measuring perfectly.
• Mounting. It reports the motion of what it is bolted to, so an under-tightened bolt, a washer that does not belong, or paint, underseal or corrosion between it and the panel damps and delays what it sees.
• Part number. A sensor that fits and plugs in may be calibrated for a different structure or model year.
• The harness. Trapped, stretched, or routed against an edge that will chafe through in a year.

So the question that finds this is narrow rather than general. "Has it been in an accident?" gets an honest and unhelpful no. "Has the bumper ever been off? Has a wing, headlight or door been replaced?" finds it — and on a second-hand vehicle the owner frequently does not know, which is why the inspection matters more than the interview.

And the failure mode this produces is the worst kind: everything passes on the bench, and the system misjudges a real crash.