If you have updated your MMI 3G firmware and didn’t unselect BOSE update, its 99% sure that after update your subwoofer and/or fader will stop working.
You cannot downgrade MMI firmware version to the previous one because bose will still do not working, and there’s also a big chance to brick the unit and lost ££££ to get it worked again.
We do offer service to fix that problem. We can do it on your driveway (everywhere in U.K.) or you can come to us.
the price will depends on distance where we have to go, also if you wish us to do firmware and maps update on your behalf – to be sure that everything will go fine.
If you have a problem with BOSE after firmware update contact us