Hello everyone, i just bought an used Nubira 2000 and the same happened to me. The radio would only work with a code and of course I did not have it. Well, I found out the code very fast. What did I do? I wrote down every single combination of 4 digits for numbers 1 - 6 on a piece of paper and tried on by one. My code was 1651.
I believe you can call or email them or even remove the frame that surrounds the audio unit. Personally I thought it was easier to try all the combinations one by one.
I have all the combinations on my computer. The file is too big to post here (1296 combinations). If you want them, send me an EMAIL and I will send the file to you so you can try one by one and save your time and money.
Nat.