So the manufacturers go to great lengths to improve to environmental performance of their cars and then tuning firms/owners fit a bypass. Very responsible. I assume the tuners/owners also fit an exhaust with the tail pipes turned down to the road which is required by cars without a DPF. I had a 170PD with a DPF and had no problems at all during the 3 years I owned the car. I now have a new 140 with the latest common rail engine and both it and the 170 have DPFs and I get better fuel comsumption that I did from the 140PD I had before the 170PD. It will interesting to see how many cars with 170PD engines with the DPF system turned off fail their MOT.