I got a 2001 volvo C70 convertible a couple weeks ago with the SC901. When I got it, all of the back speakers and subs did not work other then the passenger side back speaker. The back passenger speaker is very quiet and I can only hear it if I turn the stereo all the way up. There is no rear speaker switch and I checked all of the fuses on the amp and fuse box. What else could it be?

 

The crossover could be bad.