I have a 2004 Trailblazer LT. It doesn't have Bose (no UQA code), but it does have OnStar & rear audio controls. The stereo is a factory unit, with CD & cassette. I am getting no sounds whatsoever, including chimes or OnStar. I connected a set of headphones to the rear system and only get a static sound while adjusting the independent volume *****. I bought a new set of speakers for the front doors, but still have no sound.

The stereo appears to be working correctly, finding stations & such. Steering wheel controls operate correctly.

Head unit?

 

check the connections on the back. try connecting a speaker directly to it.