Subs suddenly producing no bass: head unit?

[nota_towel]

So I've been trying to figure out why my subs suddenly started to produce no bass. The subs and amp both work and fuses are good. RCA cables are good and head unit wiring seems OK. The reason I think it may be my head unit is when I turn the car on there a a split second of what I can describe as feedback to the subs where they are producing bass hits with no audio signal. They are normal volume but when the unit fully turns on and starts playing audio there is no bass at all. I've tried changing settings on the head unit and also trying different audio source like cd or usb audio. The subs actually produce very small amount of bass that is only detected by placing a hand on the woofer. I am stumped as to what it could be. The head unit itself is a JVC and it's about 6 years old

[430hps4]

Pull the sub out of the box, make sure the wiring from the sub to terminal is still good. Can also take a regular AA battery to the speaker wires. Hold - wire to - side of AA battery. Tap the + wire to the + side of AA battery. Should confirm sub is receiving voltage.

[nota_towel]

They still bass until audio starts coming from head unit which is why I suspect that. The speaker leads on the sub are good otherwise the sub wouldn't move at all when receiving audio because of broken circuit. Anything that I can do to fix the head unit short of buying a new one?

[naiku]

What head unit? Does it have Front / Rear / Sub RCA outputs? If so, and assuming you have a crossover on your amp, try swapping your sub RCA from the head units sub output to the rear output. If your sub starts working again, then you at least confirmed your sub RCA out from the head unit is not working, if it does not work, but other speakers work on the front / rear outputs then it is something with your sub or amp.

[nota_towel]

It ended up being the Sub RCA on the back of the head unit. I swapped it to the "front" RCA and they now produce bass like normal