Turn your ignition to RUN and your radio to OFF. Press and hold preset buttons 2 and 3 for around 5-10 seconds to obtain a scrambled version of your radio's original factory set code. Call 800-537-5140 and ignore whatever you are promted to do (something about different dealer brands Chevy, Pontiac, Saturn, etc.), And type the number 202108 into your phone and then press the # button. Input your radio's 4 digit code into your phone when prompted, then press the asterice ( * ) button (NOT pound symbol) and be ready with a pen and paper to write down the unscrambled code. Keep this code somewhere you WILL NOT lose it. Once you have the code written down, press and hold 5 and 6 on your radio's preset buttons for 5-10 seconds.
Then press the seek down button once to start the entry process.
Using the following key, repeatedly press the buttons to set your code: seek down = first digit
seek up = second digit
tune down = third digit
tune up = fourth digit
I just checked a picture of the stereo out and discovered the buttons have arrows facing left and right and not up and down. For the purposes of this process, left represents down, and right represents up.
Once you have the code entered, press AM/FM to set it.
This should unlock it. If not, may have to take a trip to local dealer.