I have the same problem. I clean all conections bit the airbag fault only dissapear when i clean with the c110cable. But after restart, the airbag light comes again. The cable looks ok and i dont have An accident before. My error is 98f5 low voltage, open circuit etc, anda sometimes 98f4 short circuit....and the same.
In the e46 is possible to clear the error with bmw scanner in the srs section bit this cant be coded in the z4
Can someone help? Thankss