Originally Posted by pbonsalb
Off at 12.2 is low. 12.6 is a fully charged battery with the car off. Of course with the car on, the alternator output will show up as the voltage, so the 13.8 does not mean much. I would be concerned about the 12.2.
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.