BMW 1 Series Reference Manual page 111

Seat position sensor in the driver's seat
Index Explanation Index Explanation
1 2
Seat position sensor Permanent magnet
The system adapts the triggering of the two airbags to the driver's and front passenger's
seat position.
Due to US legal requirements, the driver's seat and front passenger seat must be able to
detect the size of the occupant. Size is detected by the extent of back and forward seat
adjustment. In the E88, the exact position is determined by the seat position sensors in
the driver's and front passenger's seats.
The seat position detection system is designed with a dual-wire Hall sensor and is sup-
plied with power by the ACSM control unit.
The strength of the current in the seat position sensor changes depending on the seat
position and the distance of the seat position sensor from the permanent magnet.
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E88 Complete Vehicle