Cause
Faulty seat belt tension sensor
The sensor measuring tension in a seat belt, used by the restraints system to judge how an occupant is restrained. It contributes to deployment decisions — combined with the occupant weight sensor, it helps the module decide whether an airbag should fire and how firmly.
So a fault disables or restricts part of the restraint strategy, and the module illuminates the airbag warning and adopts a default. That warning is the whole symptom; nothing about the vehicle's driving changes, which is why it is easy to postpone. It should not be postponed — the lamp means the system is not fully armed.
Its position under the seat is what fails it. The harness is flexed by every seat adjustment and meets spilled liquid, dropped objects and vacuum cleaners, so a chafed lead or a disconnected plug under the seat is far commoner than a failed sensor. Never work on restraints wiring without following the manufacturer's isolation procedure, and check the connector before condemning anything.
Typically specialist work. Needs equipment or training most home workshops do not have.
Codes this can cause (2)
Codes where this is a likely explanation first, rather than merely a possible one.
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