Ok after much searching I'm really hoping someone has some ideas that aren't commonly found on basic search.
2010 E350 Sedan Base. All stock.
Out of the blue stopped at store ran inside for about 10 mins and come out to the ESC warning and Transmission square surrounding the PRNDL waa misaing. Attempted to jump start. No Change.
Battery indicating 12.7 at the time.
i had noticed for about 3 weeka leading up to event that off and on it would seem that my charging when driving would drop to 12.5 to 12.9 but then go back to 13.3 to 14.0.

Attempt to read codes and get a "not able to communicate"
Isconnect Battery put on slow charge over night, hook back up next morning and starts right up no warning no issues. Run for about 20 mins drive around block come home park. Go back to car 30 mins later and warnings are back and no start.

This becomes repeatable. Unhook charge and start. Walk away for 30 mins error comes back.

Replaced Voltage regulator. Charging solid 13.4 to 14.0 for 30 mins of driving. Feeling good stop run on store for 5 mins come out starts right up drive to doc appt. 20 mins away still charging strong. Go inside for 30 to 44 mins and come out to same error. Jump start from another running vehicle no start same error. Put new battery in. No change.
Tow home left alone for a day and a hall. Go out battery shows 12.75 on meter took a shot at cranking and started right up. WTF
Also replaced small battery in dash becauae it was probably original. (Dont think it was necessary but ruled it out)
I have not done wheel sensors just because it doesn't seem to point there but i will next before I take it to a shop.
Finally the big question is tonight it cranked after sitring for almost 2 days since last error and i didnt do anything. But i did noticed one thing tonight. After tirning off the car im standing at the front of the car with the hood closed and I here a noise that sounds like a small motor activating or deactivating. Maybe a pump shutting down. It was oddly loud enough to stand out after car was off. I would say it came from the driver's side of car. (Could be wrong)
I have never heard this small motor or pump noise or mechanism noise before and of course the error is back again.

i may have a drain on the battwry but it was 12.75 tonight but when the error is active it seems to drop lower.
I know I'm going to have to take it to a shop if i cant think of ligit options. I will replace wheel sensors before i do or anything else i can to rule out things the shop may want to take a shot at. At a much higher cost.

Thank you for any help that you may have.

 

Sounds like your ABS/ESC module wants to say good bye to you.
Get a decent scanner. Launch creader Elite for Benz. Now there is a V2.0 version. Google this W212 forum, you will find it.
Scan for codes. with it.

The yoyo charging is ON PURPOSE by design. Don't worry, it will never go away, unless you disconnect the alternator LIN data cable and your LIN plug is a single wire only.