oh yea and a lot of people have had problems with their stock kenwood sub, you might want to check the head unit, and inspect the sub, amp. check the gain, and connection...etc...
I thought I did have 6x9s in the rear deck. At first I thought it was a blown fuse but I check the fuse in the amp and its good. I also checked my deck and all the connections. I have a light on my amp so I know its getting power just no sound. Any more info?
Searcxh amn I have done a process to check out a few times. Chances say there is no way around going to the dealer though.
If the amps light is on then the going bet would be the sub is dead.