Tim Pryor

After a long string of issues with the B&O sound system on my 2014 S4 I failed to learn my lesson and got a 2018 S4 with the B&O system.
After about 6 months (2800 miles) the subwoofer stopped working. Sigh.

Symptoms: Audio sounds thin (remarkably so, like the old iPod headphones before they became 'earpods').
Going into the MMI system you can set the Sub to 0 or 100% and it sounds the same.
Changing Bass give a very small difference (0 -> full sounds like your bumping it up 1 or 2 notches instead of ~12).

I checked the fuse listing, checked the fuse marked 'Sound Amplifier' and it was good. When I pulled it there was no sound from the speakers at all.
The MMI displayed 'Subwoofer Not Available'. Upon replacing the fuse (fuse #2 left of trunk, bottom bank, second from the bottom in that bank) everything was okay and the sub works.

Notes:
I did have to reset the sound for the backup and forward sensors which you can do in the parking menu, just set the front and back to 'low' then 'medium' individually.
Also, had to reset the audio settings as they defaulted.
Be careful when replacing the fuse. The slot is energized even with the car off.

Sorry if this is like stupid-simple and a waste of your reading but I didn't find any other posts about this problem with the B9 cars. There are quite a few with the B8 and older ones but the solution is different.

Tim Pryor

Annnnd I thought the images would be hyperlinks not embedded in the thread and I haven't reached the level where I can edit my posts.
Sorry

Mr.Meme Yo Girl

why not just take it to the dealer? wouldn't it be covered under warranty?

Mikejkeil

This is a great help. I just removed my B&O sub a replaced with a JW 10 " and Alpine M500 Amp. It was working then not when i finished the install. Pulled this fuse, which is supposedly not used on 2019, and it fixed the problem. I will look to perhaps turning down the Amp gain or something to make this a permanent
fix.

Bobby Kinstle

The B&O amp checks the resistance of the subwoofer periodically to make sure it's still plugged in. Most high level inputs don't put enough load on the line, so it fails the test and then the amp turns off it's outputs. You can either add a load across the + and - of BOTH outputs (with 2 resistors less than 40 ohms) or you can use VCDS or OBD11 to disable the presence check.

keaton824

Dude, I know this post is almost 5 years old, but THANK YOU so much for posting this. I had this same issue today all of a sudden. I found your post, so I pulled the fuse, put it back and it's all working fine again. You're the best!!! Hopefully it lasts...

TT-S4

I've had intermittent sub-OFF situations since I first got my S4f, August 2018.
The dealer was NO help at all. As this was an intermittent issue, they pretty much move along if they can't repeat the problem when they are looking at it.

In my case I found that my Sub-OFF situation happens exclusively when listening to Satellite radio. Why? I have NO idea why. It is likely some wacky software issue.
After experimenting, rebooting the MMI corrects the problem, and the Sub comes back to life.
The reboot/reset is in the manual. There is a 2 or 3 button push and hold process that resets the system.

I found a much better and easier fix/es. When the Sub is not working, push the volume **** to go into "Mute", then push the **** again to return audio. Sub is back.
The other fix is to select regular FM/AM radio, and then switch back to Satellite and the Sub is back.
Very odd, I know, but it works in my case, with no need to get into the fueses.
Try it, it might work for you, and others.

keaton824

Hm, I do not use satetllite radio... Carplay pretty much exclusively, but FM radio for NPR every once in a while. I had to take my A4 to the dealership recently and mentioned this to them. They did look at the fuse and could not find anything wrong (it still has not cut out since I removed/replace that fuse anyway).

As far as resetting the MMI, I tried that multiple times before taking the fuse out and it never solved the issue for me. Messed with every setting too in the MMI as well - nothing. I guess our problems are caused by separate issues... Weird!

Mikejkeil

I ultimately fixed this by installing a NVX LOC. I was able to balance out the amp gain, MMI sub setting and LOC to get the ideal sub level. The pooping on shutdown and switching inputs went away and this has been working 100% for 2 months now. Thanks again for posting the help.

Paul_QFive

[QUOTE=Bobby Kinstle;25682789] El amplificador B&O verifica periódicamente la resistencia del subwoofer para asegurarse de que aún esté conectado. fuera de sus salidas. Puede agregar una carga a través de + y - de AMBAS salidas (con 2 resistencias de menos de 40 ohmios) o puede usar VCDS u OBD11 para desactivar la verificación de presencia.[/QUOTE
@Bobby Kinstle Can you help me and be more specific, my subwoofer turns on with almost no sound, how can I disable that verification with obd11, what option should I disable? If you can be more detailed I would greatly appreciate it.