Are you talking sometimes you get bass from the sub and other times you don't? You may have blown your sub... I'd check the wiring to it, check the resistance across the voice coils if you have a multimeter, and if you can't find anything else wrong...replace the sub. Don't use an OEM replacement or you're gonna pay out the wazoo for one. You can get a 6 1/2" Pyramid sub that will fit and sound better for under $20 shipped from Parts Express.