My factory cd player died and I was looking at aftermarket radios, but did not know if I could keep the Onstar. I went to a local car stereo place and they sold me this interface for $170, but when I went to install it I found out that it would not work with a 2002 (21/9 pin connectors). So I looked on the web and found one at Crutchfield for $99. I just finished installing everything and it works great. Their is several companies that sell the same thing. The 99-02 uses the PAC OS-1 and the 03-04 uses the PAC OS-2 (24 pin connector). It is an easy install.