DPF REGENERATION     

Diesel particulate filters DPFs reduce diesel soot emissions by 80% but they're not suitable for everyone The exhaust emissions standards for new cars have effectively required fitment of a DPF in the exhaust of diesel cars since 2009 when the 'Euro 5' standard came into force. In fact, many cars registered before 2009 will have had one fitted too in anticipation of the change in standards.Standards aim to deliver an 80% reduction in diesel particulate (soot) emissions but the technology's not without problems – AA patrols are regularly called to cars with the particulate filter warning light on indicating a partial blockage of the filter.Even if your driving isn't mainly urban/stop-start, changes to driving style may be required to keep these systems working properly. If you're buying a new car and plan to use it mainly for town-based, stop/start driving it would be wise to avoid a diesel car fitted with a Diesel Particulate Filter (DPF) because of the possible hassle of incomplete 'DPF regeneration'. dpf warning light How do they work? Diesel Particulate filters (DPF) or 'traps' do just that, they catch bits of soot in the exhaust. As with any filter they have to be emptied regularly to maintain performance. For a DPF this process is called 'regeneration' – the collected soot is burnt off at high temperature to leave only a tiny ash residue. Regeneration is either passive or active Passive regeneration Passive regeneration takes place automatically on motorway-type runs when the exhaust temperature is high. Because many cars don't get this sort of use car manufacturers have to design-in 'active' regeneration where the engine management computer (ECU) takes control of the process. Active regeneration When the soot loading in the filter reaches a set limit (about 45%) the ECU will initiate post combustion fuel injection to increase the exhaust temperature and trigger regeneration. If the journey is a bit stop/start or you take your foot off the accelerator while the regeneration is in progress, it may not complete and the warning light will come on to show that the filter is partially blocked. It should be possible to start a complete regeneration and clear the warning light by driving for 10 minutes or so at speeds greater than 40mph. If the regeneration is unsuccessful the extra fuel injected will not burn and will drain into the sump. Oil quality will deteriorate as a result of this and the level will rise. It is important that you check that the oil level does not increase above the maximum level on the dipstick as diesel engines can run on excess engine oil – often to the point of destruction. If you ignore the warning light and keep driving in a relatively slow, stop/start pattern, soot loading will continue to build up until around 75% when you can expect to see other dashboard warning lights come on too. At this point driving at speed alone will not be enough and you will have to take the car to a dealer for regeneration. Expensive repairs If you continue to ignore warnings and soot loading keeps increasing then the car won’t run properly and the most likely outcome will be that you will have to get a new DPF costing at least £1000.