Seat belt tensioner (BMW 5 Series E39)

The seat belt tensioner is integrated into the front seat. In the event of a frontal collision, it ensures that the seat belt fits tightly against the body and thus prevents the body from slipping downwards from under the belt. The seat belt tensioner is triggered in the event of a severe frontal collision by the electronic airbag/belt tensioner control unit. Depending on the severity of the collision, the control unit activates either only the belt tensioner or also the airbag. On command from the control unit, a small pyrotechnic cartridge is ignited in the belt tensioner. The gases formed as a result of the explosion move a piston forward in the belt tensioner tube, which is connected to the belt buckle by a cable. The belt buckle is pulled downwards and the free play of the chest and lap belt straps is reduced. When the seat belt tensioner is triggered, the airbag/belt tensioner indicator light is permanently illuminated. In this case, the seat belts function in the same way as if the belt tensioner were not installed.

The seat belt tensioner does not require maintenance. After activation, it must be replaced as a set.

Caution: Before disposing of a tensioner that has not been activated, it must be forced into operation in the set position (workshop work).

Caution: To avoid unwanted operation of the belt tensioner, it is necessary to follow safety precautions.