Not really related, but do the TDI Volkswagens use a DPF? My mother has a 2010 TDI Jetta and the exhaust pipe is just as clean as factory, with about 10,000 miles on it. It is as clean running of a car as the Cummins with the DPF. You cannot even smell the exhaust if you stick your nose up to the pipe with the car running. I looked under the car and only saw one catalyst device, not the three that the Cummins has.