I had a quick lesson on DPFs this week. On the big trucks there will be a manual override "button" so the self cleaning can be delayed to a "more appropriate time", eg a garbage truck at the dump site. I also got to briefly see a DPF in action on a test engine. The exh pipe was pointed up and NO smoke at was coming from it but it sure was hot. The engine, a 450 HP ISL ( 9 litre ) on a training module was running inside a shop with no exh flex hooked up to the shop exhaust system. The inside of the tail pipe was a clean as a new pipe off the shelf. Once the DPF had cooled down ( from 1100*F ) the inlet pipe was removed and it was as black as ever but the outlet was clean. Now thats what I like to see, a diesel with 450 HP and no smoke. There was no real stench either. Shadrach