Originally Posted by Mike Benvo
It's not ideal but not a concern at 12.2.
12.2 is strong enough. My car has had between 12.0 and 12.2 for over a year and it's just fine.
Sometimes it will drop slightly under that. 11.8ish and under is when these cars get a little upset.
With the car on, it does mean much. It was a test to make sure his alternator was working properly, which at 13.8, it is.
OP: You should find a tool to read the freezeframe data of the fault code. That way you can see the conditions under which that fault was triggered.
A car battery at 12.2v is considered 50% charged. If that is all the charge it is taking, it is on its way out. I would be surprised if you could start one of these M3s with the battery at 12.0v.