I do a regular 280 mile journey of which over 200 are on the motorway (typical lane 3 speeds). My last stop was about 20 miles before the end of the journey, and when I stopped at my destination the fan came on. I've never noticed a regeneration before in 50,000 miles and 5 years of ownership, but could this be what it is, and what's the best thing to do now I've interrupted it? Forgot to say that final minute or so is crawling at idle in 2nd gear. (Allows turbo to simmer whilst on a dirt track).