Take the car to the dealer and get out your wallet. GM stopped allowing us to buy radio service manuals after the '94 model year because they wanted to lock up all that repair business for themselves. The dealers are limited now to their two grossly over-priced authorized repair centers. The radio will also have to be reprogrammed to the car when it is reinstalled. It can not be replaced with a higher-quality aftermarket replacement because GM cleverly built the Body Computer into it to make sure you pay the very high repair cost.