If you've ever had to disconnect the battery, or locked your stock GM radio by some other means and don't have the unlock code - here's what you need to do to get it unlocked. Sorry I don't have any photos, but if you can't find the radio - or any of the buttons...I'm not sure any amount of pictures would help you.
Press & hold the 2 & 3 buttons at the same time for about 10 seconds; a 2 or 3 digit code will appear, write this # down, press & hold the am/fm button for about 10 seconds: another code will appear, write this # down, then call 1-800-537-5140 and enter 202108 (this is a dealer code - you can use one of the others below, too) followed by the # key, then enter the numbers that you wrote down, followed by the * key.
The call will give you a 3 or 4 digit override code. Write this code down so you have it if you ever need it again. Enter this number into your radio following the instructions in your owners manual.
Note: If you get an override code that starts with 0, you drop the 0 when entering the code into your radio.
If you don't have an owners manual, then press & hold the hour button until the first 2 digits of your code come up, then press & hold the minute button until the last 2 digits show. Then press the am/fm button.
Repeat step #5 twice in a row it will disable the Theftlock and you will see "---". You will then be able to change to a new lock code.
IMPORTANT - Other dealer codes: 139010, 206053 and 620529 - these may be inactive by now; GM will remove them from time to time if they feel that they are "compromised".
Also - there are 2 modes to the TheftLock - "LOC" or "SEC" and "INOP". Once the anti-theft is activated, the radio display will show "LOC" or "SEC" - you then have 8 attempts to enter your code. If after 8 attempts you don't enter the correct code, the display will change to "INOP". It is only at this time that you will need to wait one hour, with the ignition ON; before you can retry. After that - you will have only 3 attempts before the radio enters "INOP" mode again.