After countless posts, and reading others countless posts, I've finally figured out why the mach 460 bass quits working! Most peoples answer is to gut the system and replace, I like to fix things that are broke instead of just replacing them just because I can't figure it out. So here we go! After replacing the head unit, under dash amp (twice), and having the wiring all rung, I found out that the rear amp on the driver side was bad! If you lose your bass, it's more than likely your rear amp, or amps have went bad. The amp under the dash only controls your high end, while the amps in the rear control the low end, replacing your head unit, or under dash amp won't fix a thing. I hope this helps out alot of you guys whom I saw had the same problem as I did, but couldn't figure out why! Take care all!