Had an interesting DEF issue arise yesterday. Out of the blue got an 'incorrect fluid' warning, with 200 miles to no-start, and a 'check engine' light. Naturally, I was well over 200 miles from home or a BMW dealer in the middle of the Sierra Nevadas. The car has not been in for service for almost a year, in fact it is due for one; I topped off the DEF thinking it may just be low, but the countdown persisted for another ~75 miles, then disappeared. 'Check engine' light is still on.