Hi Caroline this is a long shot that you get this post as the thread is now 2 month old but I have seen this problem before, sold a E90 320d to a guy and he was back time and again with the same issues as you and just couldn't get to the bottom of it. Most diesels get run on supermarket rubbish diesel and never really get a good hard run often and mostly just potter around cities, short journeys etc and the dpf filter never gets a chance to carry out a full regen, they have to get massively hot, manifolds just get clogged with debris, diesel is just a filthy fuel. Carry out the above advice that you have received, get the fault codes cleared then fill it with good branded fuel, find a motorway keep the revs above 2500 rpm and go for a drive 100 miles round trip, when I did this to the 320d I could see the car do the regen process on the road, the crap that was leaving the exhaust wasn't pretty but it worked, the car was running smother more responsive etc, 4 months passed and back the guy came, codes were cleared told him what to do and that has been more that a year now, he just makes a point of doing a journey every 6 weeks or so. Hope this helps or you have maybe just got fed up and sold it. Regards Stephen