I think you are referring to is the seat mat sensor. I'm pretty sure that this isn't the problem with my car because the seat mat seems to be functioning as it should. (seatbelt light comes on when passenger sits on seat without wearing seatbelt)
Also, people who have had this problem have reported error messages regarding the 'restraint system'. I do not have this error.

I have read about the bypass that you are referring to, but this is apparently a fix for an open circuit. I doubt my seat mat has an open circuit because it knows when there is and isn't weight on the seat.

 

I will check the connections as DIS suggests. Is it worth replacing the pretensioner?

 

Cheap and easy bypass, once you get the module just cut the plugged in end from under your seat of the oc3 mat solder that part onto the new bypass module and itll all be good

https://5series.net/forums/topic/118...3#entry1391653

 

I have seen this type of bypass, but I can't be sure that my seat mat is faulty because the fault description in DIS doesn't mention it.

 

I have checked for any damage to the wiring under the drivers seat and then cleared the codes again and it has stayed off since saturday. I wonder if it was just a dodgy connection on one of the plugs. (I disconnected and reconnected them when checking for damage)