Radio

GM's silly theft-lock system. It's designed to separate you from your money. Visit the dealer. They will retrieve the code, call their secret phone number to translate it to the unlock code, punch that in and unlock the radio, ... For a fee.

It's understood to prevent the many computers from locking up, always use a "memory saver" when disconnecting the battery. This is even worse and much more costly on Volksawagens. There are many normal repairs that require disconnecting the battery, and the manufacturers planned ahead for that by making these things happen so you have to go back to the dealer.