I guess this is one of the first locking radios ever at gm

https://www.youtube.com/watch?v=u2osiPwVNm8


http://chevroletforum.com/forum/tahoe-suburban-25/%22l-o-c-%22-stereo-screen-menu-17934/


try googling this, see what others did,

only GM can unlock this rad, call them.

there may be hacking sites that can but i dont use or trust them.