BMW E39 airbag light on: the most common causes
Why is the E39 airbag light on?
The most common causes are the front passenger seat occupancy mat, the connectors under the seat, the seat belt tensioner circuit and the belt buckle switch. A side impact sensor or the control unit can also be faulty. The fault code tells you which direction to look in.
What does fault code 240 mean?
Code 240 indicates that the airbag control unit is not working. The code cannot be cleared; the unit must be replaced and coded to the car. Airbag work belongs at a workshop: let the workshop do it.
The airbag light is on only briefly after starting or when someone sits on the seat. What is the fault?
A typical cause is a break in the wire of the front passenger seat occupancy mat or its connector. The fault code is seat occupied recognition. Airbag faults do not go out by themselves, they must be reset with a diagnostic tool. Let the workshop do the check and repair.
Can the airbag light come on without a fault code?
Yes. Sometimes the light comes on as the temperature rises without a code being stored, and the cause has been the control unit. Then reading the codes alone is not enough, so troubleshooting is best left to a workshop.