1998 GMC Van Radio locked

You got caught with one of the tricks designed in to cost you money after the sale. You have to visit the dealer for the code. There is a series of buttons to press to get the first code out, then they have to call their 800 number to translate it to the new code. They don't make that phone call for free.

I forgot to mention, due to their design, these generators have a huge problem with voltage spikes. It's common to go through four to six replacements in the life of the vehicle. To reduce the number of repeat failures, replace the battery at the same time unless it is less than about two years old. Part of their job is to dampen and absorb those spikes, and they lose their ability to do that as they age.