Your radio will require input of it's "code". IF for some reason you don't have it your radio will be useless; Don't fret though, with proof of ownership (vehicle registration in YOUR name) and the serial # of your radio, a BMW dealer can secure your radio code for you. Anybody knows if there is a time limit to change a battery on a 1990 735 il? I am doing mine for the first time tommorow and I don't know if the OBC will be affected. Looking forward to hear from you guys. Thanks.