or course its a mot failure ie visual test,
so when we get a car in with dpf blocked at say 40.000 miles been used in town all its life never really gets to run around 3000 revs for a 45 minutes time span at least to clear the dpf, we would force a regen on that car all car makers except mini allow the software to force a regen on the spot where the engine is reved at 3400 revs for 45 minutes and the ecu fuels it to force the exhaust dpf filter etc to around 650 degrees or more and create a furnace effect in the filter, this cause massive heat and pressure within the exhaust and the turbo even in side the engine etc. mini do it completely differently ie the software will force a reg ti the car the next time its driven on the road,,,trouble is it still takes 45 minutes of over 3000 revs or more to do the process, you try driving any car at those revs all the time on the road unless its started at a motorway maybe, then add a engine that 125,000 miles is already at a point of end of life from worn parts and things break with all this pressure see it all the time with dpf diesels and bad outcomes on all brands,, also every time a regen happens its leaves a tiny bit of brown fine sand in the filter this is what blocks them as its not a free through filter its a saturation filter to catch the particles,
diesels with dpf filter are happy on motorway revs at 2500 or above 20 miles each way ie get chance to get to hot temps so the system can deal with the soot, and then the reason why anyone buys a diesel is mpg and to gain the best low revs high torque is why most buy a diesel in first place,, ironically a dpf filter is only 100% when its new and by time 40k comes along its causing more pollution than what it is meant to stop from cars clogged up and cars driving around at higher revs trying to keep them clear, or the partially blocked ones that cause fuelling and more pollution from not working correctly,, euro 5 diesels have got it more right with addblue additive, but euro 4 and 5 have always been a pain to live with,