So in the past few months, I've taken my A6 TDI on quite a few 500+ mile drives and recently my mileage has been about 25% lower than what I used to be getting. I have tried everything in the tips for better mileage and those do help just a little bit, but I would like my old mileage back. For example, on a flat and straight road with no wind, I will get about 29 to 32 mpg, cruse control on 75 or 80 mph on my local 150 mile straight and flat stretch, both ways. The instant mpg meter wouldn't even touch the 40mpg tick mark. Here's the interesting bit - if my car starts doing a regen, the mileage shoots up to 40-50 mpg for the duration of the regen! My average mileage would increase significantly as well. It's the mileage that I would usually see about a year ago when I first bought the car. Obd11 shows no trouble codes with my car, and my dealer says I must have one for them to do any warranty work on it, otherwise I'll have to pay a $300 diagnostic fee if they can't find anything physically broken. I have less than 10k miles left on my dieselgate warranty which means it will be over by fall of '22 at my rate. Has anyone had this problem before, or know of a way to force a check engine light for the DPF? The only red flag I've seen in obd11 is that my car averages 296 miles between each regen.