Stereo Issue: Fade & Balance Don't Work Any More

[whitemountaingmc]

All of a sudden I've lost sound from all but the front left speaker in my 2004 2500HD. Both balance and fade have no effect any more. It was fine just a few days ago and I know of nothing that's happened to create this issue.

I imagine that getting a dealer to look into this will turn out expensive. Just getting to the thing must be a hassle.

Any ideas?