No RCA voltage?

I have a problem, I was hooking up my amp, to make sure it works. Well, I grabs one of my subs to make sure it had output. I hooked it up, turned the car on, and the song was playing, but no sound or anything from the sub. Well, I grabbed my DMM and attempted to read the output voltage, to see if it was just the sub. Nothing. Then proceeded to check the RCA voltage, nothing again. Pulled the HU out, and checked there, nothing. I don't get it, 'cause I had my last amp hooked up, and everything was great, played fine and everything. It's been about a month, I go and try to hook up my new amp, and no RCA's. My headunit is a Pioneer DEH-P9. Any ideas?