Just to chime in again, I've continued to have the random bluetooth failures that others here in this thread have discussed. Like FelixCatus, I have found that when bluetooth is "out", I cannot turn it off (or back on) via the headunit (I don't have iDrive but instead use the headunit controls under /Configure/Phone). The car shows my paired phone, but cannot seem to use bluetooth to connect to the phone.
I too have done various tests to determine that it's not the phone's bluetooth that is non-functional. It's the car. SOS is working and throws no errors.
I have found that these problems seem to come up when my car has been into the dealer for anything that requires a battery disconnect (which is most anything) or software upgrade. But bluetooth failure also seems to happen randomly. In nearly every case, it will "reappear" after I have had the car turned off for at least 30 minutes. Then, it will work fine again....until it doesn't.
I should note that one time it did this (failed) when I was leaving the dealer after having a repair done (to the sunroof) that required software/reprogramming. As I was getting ready to drive off, I noticed that bluetooth was dead...so I called the SA back out. He couldn't get my phone or his own phone to pair, so he got the mechanic back involved. After another hour to reflash the software, and "cycling the power" (disconnecting the battery I guess), it came back. I asked for an explanation and was told "Oh, all of these things are finicky and sometimes it takes some fiddling to get them back online." Riiiiiiiight.
It's a maddening problem and one that I fear won't be addressed by the dealer as diagnosis requires a lot of fiddling and occurs randomly. This of course is exactly the sort of problem that results in a "bring it back when it's doing it again" result....which of course is super-inconvenient unless one lives next door to the dealer. ;-)
So, the question...has anyone here who has had bluetooth problems (such as those described in this thread) been able to VERIFY that replacing the TCU fixes the problem? If I knew that was the case, I'd go fight for a TCU replacement and not put up with the "mess with you until you give up trying" tactics of the typical dealer.