A recent article in Autocar magazine about the criteria needed before a diesel is able to go through its regen procedure stated that there has to be a minimum 20 litres of diesel in the tank. This is because the procedure uses extra fuel to get the engine up to the required high temperature. For a 150 that is spending a lot of time on short urban journeys, and especially in winter, this means that the tank should be topped up with about 200 miles remaining shown which is a lot sooner than most people would usually do it. I wonder if anyone has any further info on this with particular regard to VW diesels.