Sitzbelegungserkennungsmodul defekt

The module that decides who is in the passenger seat — an adult, a small adult, a child, a child seat, or nobody — and tells the restraints module what to do about it. It reads a mat of weight sensors in the seat cushion, and on many vehicles the seat belt tension too.

The reason it exists is a lesson the industry paid for. Early airbags deployed at one force for everyone and injured or killed children and small adults in crashes that would otherwise have been survivable. A bag inflating at three hundred kilometres an hour into somebody sitting close to it is a weapon, so the system has to know who is there before it decides what to do.

It is blamed far more often than it fails. The commonest cause of a classification fault is not the module but the load it is reading: a heavy seat cover, a cushion, an aftermarket heater pad, or something wedged under the seat. Next commonest is the harness beneath the cushion, which flexes on every seat adjustment. Remove everything from the seat and check the wiring before condemning the module.

And it is calibrated to the seat it was installed in. A seat removed and refitted — for a repair, a retrim, or a used replacement — very often needs the classification recalibrating with a scan tool afterwards, which is a step easily missed and a fault easily misread as a failed part.