If the car is repeatedly used for short runs, DPFs do not passively regenerate (do not burn off the soot they collect) and then either get clogged up or have to 'actively regenerate' using diesel fuel pumped in via the engine. If they are repeatedly switched off mid active regeneration, then the engine sump oil becomes contaminated with diesel. Even if the car is run distances so the DPF regenerates properly, it will start filling up with ash from the burned soot by around 80,000 miles and will either need to be chemically cleaned by the Ceramex process (about £400), or replaced, and a replacement can cost £800 - £1500. Here's everything you need to know about DPFs in a bit more detail: www.honestjohn.co.uk/news/miscellaneous/2017-10/ev.../