Michael, do you have sound from the rest of the speakers? Is it only the sub not working?

If yes, I suggest u check the connections one by one as follows:
- Cables going to the sub
- The tapping on the OEM amp plug (u should have four cables/connections to check)
- Speaker level input or RCA input going to the Alpine
- The remote power cable going to the Alpine
- The main power cable going to the Alpine
- and finally the ground.

Bad grounding can make no sound even if the amp is showing the ON blue light.

Good luck!

__________________
BMW 1M 2012 - Current
Jeep Grand Cherokee Limited 2011 - Current
BMW E93 330i Convertible 2009 - Sold
BMW E46 320i 2004 - Sold
BMW X5 4.4i 2002 - Sold
VW Golf GTI 2000 - Sold
BMW 740i 1996 - Sold