plasma

Started getting the consumers electronics turned off error. Also noticed AC goes into limp mode. I figured the 2 year old battery was dying. So I setup in the hud to monitor voltages. With car off, the battery is around 12.1 volts. When the car starts, it drops to ~10 volts, but quickly goes up to 11.9. After a few minutes of driving, the volts start to drop.. 11.8, 11.7 etc. once it hit 11.2, I got the red "Brake Malfunction" error accompanied by loud beeps. Stopped the car. Restart was sluggish but started. After I got home and let the car sit, the battery is back up to ~12 volts.

To me this is the alternator. But could it be a bad battery or faulty regulator?

rapidoxidation

As I understand it, the regulator is part of the alternator. If it was mine, I'd replace the alternator and be done with it rather than have to do the job twice (replace the regulator then replace the alternator later). I bet your battery is fine.

Charge your batteries (main and aux) so you're not placing a huge load on the new alternator once it's installed.
Edit: Your aux battery is fairly new too, right?

mtrevelino

I say it is the regulator. Make sure you get a Bosch regulator. You may have issues with any other brand.
Mike T.

kajtek1

When it would be good idea to calibrate the meter with reading at battery post, anything below 13V means there is no charge.
Replacing VR is common and easy thing to do.