Engine On and Off system
 

I have a 2016 A6 Premium Plus with the engine ON and Off feature. That's when the engine shuts off when at stop lights and then starts up when you take your foot off the brake.
It doesn't work. I had the dealer look at it and they said that you have to turn all features off (radio, heater/air, etc) so the battery as enough power for the feature. they said my battery was in good shape but even a slight drag on the battery makes the on and off inoperable. Sounds to me technician talk for "we don't have a clue!" We also have an A4 and the on / off system works well with radio and heater on.

Anybody have any advice on this?