Belt buckle sensor
The front seat-belt buckles are equipped with sensors which detect if the seat-belt buckle is fastened or unfastened. Using information from the seat-belt buckle sensors and seat position sensors, the airbag control module determines how the belt tensioner detonation circuits should be activated. The front belt tensioners can be activated individually while the tensioners for the outer rear seat passengers are always activated simultaneously with at least one of the front belt tensioners.
The seat-belt buckle sensors consist of a Hall sensor (1) containing a circuit board and a magnet (2) which is mounted in front of the Hall sensor on the belt mechanism. The sensor detects the magnetic field generated by the fixed magnet.
When the belt tongue (3) is not inside the buckle, the magnet (2) lies near the sensor. When the tongue is fastened, the magnet (2) is moved from the Hall sensor and the magnetic field is altered.
- Unfastened: 4.0-7.0 mA
- Fastened: 12.0-15.0 mA
The airbag control module provides voltage to the Hall sensor every 100 ms while simultaneously measuring the amount of current passing through the sensor. The current passing through the Hall sensor is dependent on the magnetic field that affects the sensor. The airbag control module sends out a bus message and the BCM uses this information in order to switch on the seat-belt warning.