I have a Pioneer DEH-5900IB that worked fine in the last car i had it in, and everything else in my current car worked fine with the last CD player I had, but after I did the switch, my sub out and rear speakers don't work. I know that it is not the grounding for the amp. Good clean ground and it has never been a problem. The RCA cable is not the issue because i can move the RCA to the rear speaker output instead of the sub out and it works fine. Why would the sub out just "stop" working out of nowhere? it was working fine when the cd player was in my sister's car, but once we took it out, and switched cars....now the sub out decided it doesn't want to work. And yes, the sub setting in the menu has the sub on.