Sorry to bump an old thread, but this happened to me on my 2011 yesterday. It seemed to be triggered by me trying to lower the fan speed at startup (using the dashboard buttons, not the touch screen) at the same moment the rear-view camera was trying to pop up. The fan got stuck on the setting it was at (around 90%) and refused to shut off no matter what, even when I turned the car off, restarted, etc etc.
I got to work and left the car in the parking lot hoping that the fan would eventually turn itself off... Then I forgot about it. It did not. I came out a few hours later to a flat dead 12V battery and a Volt that wouldn't power up as a result.
I had my son drive down and give me a boost which got the car up and running again but the fan was STILL stuck on. I also got a "service battery charging system" error on the dash as I expected, but it quickly went away once the HV battery started replenishing the LV battery.
I then did a battery disconnect for about 5 minutes, reconnected...and the problem was solved.
I suspect that this was a simple CANBUS error that caused the HVAC module to loose communication, perhaps triggered by a software bug that allowed the fan speed request to clash with the shift lever request to activate the backup camera. I have noticed HVAC related oddities that seem to occur in correllation to the backup camera before if you push a dash button at the wrong time, but it usually just results in a solid blue screen that goes away with w restart, but this is the first time I experienced this fan issue.
Anyhow, a complete reboot solved things.
For anyone finding this thread and looking for future reference, a dealer visit isn't necessary. Pop the hatch, access the battery, disconnect the ground for a few minutes, reconnect.