I have own a 2010 Traverse LT AWD. I have had many major issues with this that have been since taken care of. Now I’m having trouble with left speakers just out of the blue. Only left speaker working is the front left tweeter. front door and rear left door are no longer working. When I adjust left-right and front-back on radio all work but the left front door and left back door speakers. Is there a fuse possibly that has gone out? Just one day, a few weeks ago, I got in to go to work and there was nothing on the left side but the tweeter. Very frustrating.
Ask your shop to double check the wiring to the speakers is ok, the speakers aren’t wet, the radio unit is getting proper power, etc. If that all checks out the problem is likely a faulty radio unit. I’m not familiar with the wiring diagram but since the radio works otherwise I doubt the problem is fuses. Is there any media source that you can play where the speakers work correctly?
GM uses cheap $10 chinese speakers in their base radios and eventually you have to replace them . Have a 2008 Envoy and I have replaced all 4 speakers in due them failing . Replace them all and be done with it . I installed 4 decent Pioneer speakers and have never had another issue .
Do your speaker covers say “Bose” on them? If so, it will be a loose RCA connector on the amp under the center console. They have a history.