Unexplained drop in oil level

A6 All/ S6 All
#1

I got “low oil level” warning last week after driving up into the mountains to ski. I added 750ml - but the oil level was steady for the 1000+ mi prior to that.

Co-incidentally, this had happened twice last year (to a different mountain) before I later discovered I had a torn membrane in my oil separator-and a whole lot of oil sitting in the IM. Both have been repaired last Dec.

I did notice there is a slight vacuum in the oil cap at idle. Nothing noticeable with the dip stick, though. No misfires, the only engine code I get is:

Engine
Part #: 4F1910552A
Component: 5.2L V10/4V FSI
Coding: 01050009190F0260 (hex)
Fault codes:
P1647 Please check coding of ECUs in Data Bus Powertrain

Thoughts?

#2

Its very normal to consume a good amount of oil on long road trips where the car is at a steady rpm for a while and the vac dips into the -15 range for a long time. It is the work of the PCV system pulling oil out of the valve covers and crank case with enough vacuum to pull it into the motor.