I understand you have recently written on the subject of DPFs. My particular experience of the current X-Trail diesel (and my ongoing quarrel with Nissan) is that the first time the warning light came on, the self-cleaning system worked, but the second and third time it didn't. As the X-Trail is still under guarantee, the dealer regenerated the filter at Nissan's cost at the second incidence, but refused the third time. In conversations with the dealer and with Nissan Rickmansworth, Nissan took the line that it is not a warranty issue and the first cleaning was a favour. The second, despite my protests, cost around £165 and lasted more than a working day. The explanation is operating conditions: either my driving style or my local roads, which do not allow speeds much over 40 mph. I counter that there is nothing about this in the driver’s manual - only what to do when the warning light appears, and that additional operating costs currently running at £165 per month make the car unfit for my purpose. Apart from any advice you may be able to give regarding my approach to Nissan, I wonder if you have broader information on the car industry's problems with the fairly recent introduction of DPFs and their warning and self-cleaning systems?