I have a Pioneer DEH-P6000UB and my buddy has the same HU in his car. I found a system on Craigslist and had him run and get it because I was still at work. He hooked the system up in his car to make sure it worked and met me at my house after work. Everything worked but there was an odd issue where the amp/sub would not come on until the volume was at around 30, then when you lower the volume under 30 it shuts off. So we hooked it all up in my car and it worked fine so we assumed it must be something with his car. Well I went to shut the subwoofer off on my HU and that didn't work so I realized when my buddy hooked the wires up to my HU he didn't hook the RCAs to the subwoofer output. So I pulled the HU and put the RCAs in the correct spot and it started doing the same thing in my car where the volume needs to be at 30 for the amp to come on. Now this makes me think there's something not set up right with the HU sense we both have the same deck. Sorry for the long thread but has anyone ever experienced this or have a clue what's going on? I would like to have my sub amp connected to the sub output so I can control it and hook my 4 channel up.