The Regen is there to burn if extra soot trapped in the exhaust system. All modern diesels have them. You may not notice every time you go through a Regen. I only notice it when my window is down or I pull into the garage and turn it off and I can smell it as i get out. Doesn't really smell bad, just different, like really hot metal as it has to heat up to over 400 degrees I believe. Sent from my Pixel 2 using Tapatalk