After three trouble free years, the diesel has decided to camp in a service bay for couple of days.
Just two weeks after the annual service/oil change, including refilling the two urea tanks with Diesel Exhaust Fluid (DEF), and on our first long trip in the US (after returning from Germany) we get a warning: "Incorrect DEF." This is quite different from the more common "Low DEF," which allows 999 miles to replenish the supply before disabling restart. This disables restart after 180 miles, apparently figuring you are trying to violently circumvent federal emissions laws!
The DEF is of course full, and the correct chemical. Hard to do much travel with a car disabling problem.
So far, they've tried replacing two of the NOX emissions sensors, and reflashed the emissions firmware, and left everything to sit overnight for a cold restart of all the modules.
We just happened to be near a larger dealership (BMW of Minnetonka, Minnesota), and it is the first time their service team has seen this problem. They currently have it as an 'escalated issue' with BMW NA.
Maybe I've just been lucky, but touring, towing, cruising and bragging about 29 MPG have all been great up to now. Just hope I'm not going to break that streak for long.