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Home >> BMW >> 2012 >> 335xi Automatic Trans >> Repair and Diagnosis >> Restraints >> Restraints Control Systems >> Restraint System - Functional Description - E92 >> Restraints Systems - Functional Description >> Seat Belts >> Belt buckle switch
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Belt buckle switch

The belt buckle switches indicate whether the seat belts have been fastened or not. The belt buckle switches are supplied with clocked voltage by the airbag control unit. The following shows the voltage curve that is measured at the airbag control unit when the voltage curve is OK. For the voltage measurement, the adapter lead must not be connected to the seat belt buckle switch!

Fig 1: Display - Belt Buckle Switch Signal Screen
G09841635Courtesy of BMW OF NORTH AMERICA, INC.

Test image for oscilloscope measurement 

NOTE: Never perform any work on the airbag unless the vehicle battery has first been disconnected!Always ensure that the battery is disconnected before connecting or disconnecting the plugs for the airbag control unit, sensors or gas generators!The airbag control unit contains vehicle-specific data and must be encoded prior to operation!Removal and installation in other vehicles is strictly prohibited!