it probably requires a code. You'll need to contact the dealer if it is not in the owners manual.
The code is radio specific, so you wont be able to get it elsewhere.
<span style='color:gray'><span style='font-family:Courier'>1995 e36 3 Series RIP
1999 e46 3 Series BURN IN HELL
2000 MR-S Roadster= Current</span></span>