So i recently got an 04 sierra, when i bought it it didn't have a radio. Rather than buying a new one i wanted to just throw the factory one from my Tahoe in but the vin lock prevented that so i found out a permanent fix that only takes a few minutes. Step 1:Remove the cover on the bottom of the radio. Remove the screws (if any) then pry the plate off with a flat tip, it doesn't take much force. Step 2:Remove Tape deck or whatever is covering the board. Step 3:Locate the black chip (pictured) The two ive seen start with a nine and are approximately 7 numbers long. Step 4:Remove the chip, I used some needle nose pliers and wiggled it back and forth til the joints broke, it worked fine for the two ive done. You can be more professional and careful but it didn't matter to me. Step 5:Reassemble and plug it in. When you start the vehicle you will get a message on it that says calibration error, hit the power button and your good to go. This should work for all the 00-06 GM radios, i did it with the tape deck and CD player one and the 6 disk changer one and they both work.