'12 TL Base 3.5L, 55k.

So, with the cold weather we had this week, I telecommuted and avoided driving when it was -20+F, but did take a couple trips at -10F that caused the maintenance minder to show a "check charging system" message and illuminate the battery light. Subsequent trips yesterday and today (up to the mid-teens!) caused the "low battery voltage" warning to come up, but that went away on its own today.

On my way home from work today, I hooked up my wifi ODB-II reader and graphed the system voltages. It read a steady 13.8v as long as the car was moving. Stopping/idling dropped it to 13.0-13.2. There was one takeoff from a dead stop that briefly showed 11.4v, but I kinda figured that was a goofed reading or something, because I couldn't duplicate it. My understanding is that the ECU reads voltages 0.2-0.5v lower than what I would read at the terminals with a multimeter, if I could find my darned multimeter. ;-)

I am also hearing an odd whining noise I didn't remember hearing before, it's only really audible <15mph but it pitches up and down w/ rpm. Sounds sorta like a vacuum cleaner running in down the hall or something.

Are these voltages normal?
Could the extreme cold have damaged a pulley or bearing or something? (Causing the noise.)
I am seeing no error/trouble codes to reset, so am wondering how I might reset the Charging System warning to see if it pops up again?
The app I have shows raw data from the sensors, but not which sensor is which. Is there a guide for that somewhere?

Thanks!

 

Ran errands this morning. After the third start, the error didn't come back, and the noise went away at some point too.

It's like the darn car is running Windows: Millennium Edition. I think it's telling me to move somewhere warm.

 

Chances are it's your alternator on it's way out. I'd get your alternator checked. I experienced similar, where i heard high pitched noises on and off for a few months. Then one day my check charging light came on, only mine never went away. The car died later the same day, but thankfully, i had just made it to my mech's parking lot. I think charging voltage at battery should be 14.7V.

 

Agree with alternator.

 

Fiddlesticks.

 

95% chance it's the alternator. Alternators often start acting funny when they're on their way out rather than dying altogether. Regardless of load, idling, etc., you should be seeing a constant 13.7V - 14.2V when viewing from the OBD. The 13-0V - 13.2V and especially the <12V is definitely no bueno.

The whining noise is almost certainly the alternator diode on its way out. It could be a bearing as well but more likely the diode. I had the exact same situation at about 150K miles. Whining/whistling noise from under the hood with voltages dropping to around 12.0V - 12.4V. You can replace just the electronics board on the alternator but it's about the same price as replacing the entire alternator. I just replaced mine with a Duralast from Autozone since they have a lifetime warranty and an alternator only takes about an hour to change. I figured if it dies, I'll just get a new one for free . After 35K miles it's still going strong.

It's from a BMW but there are lots of videos and articles online