Stereo Sound limited

I have a Pioneer head unit in my 02 Av, has been working great, but all of a sudden the sound is very low, i have to turn the fade almost all the way to front balance in order to get any volume, any ideas?

Sounds like you might have a voice coil going out on one of the rear speakers or a loose wire causing it to short out the rear channels. Could also be an internal problem with the head unit.