I have the Avic D3, and the sub pounds hard, however, I cannot control the sub level in the D3 sound menu. I cannot turn off the sub by pushing the off button either.

I had this HU installed for me, but I'm fairly comfortable pulling it out and checking wires. Is it a wiring issue?

Did you try resetting your unit ?

i had previously removed the unit to do the bypass. Would that reset it? It wasn't working even before I removed it.

i think the sub is wired off the wrong RCA's

cut in the HPF

try the fader

or it may be off the speaker leads.