What is a DPF?
A Diesel Particulate Filter (DPF), also known as FAP on some French vehicles, is a device fitted to the exhaust system of modern diesel vehicles to reduce emissions and meet European emission standards. It does this by trapping soot (Particulate Matter – PM) from the exhaust gasses while letting the gasses flow through the system.
As with any type of filter a Particulate Filter needs to be cleaned regularly to function properly. With DPF’s this is done by a process known as Regeneration which involves a combination of a catalyst function in the system and burning the soot to gas at a very high temperature leaving behind an ash residue within the DPF. Regeneration should be an automatic process taking place in the normal use of your vehicle. You may have noticed this in the form of a blast of white smoke form the exhaust on occasions.
DPFs have been in common use in passenger cars and light commercials from around 2003 in preparation for Euro 4 regs (2005), with Peugeot, Renault and BMW being early takers. Euro 5 (2009) made it compulsory for diesel cars and light commercials to have a DPF fitted and Euro 6 2014 will tighten this up further.
What problems are encountered with a DPF?
If regeneration doesn’t function properly it leads to a build-up of soot affecting performance and fuel economy. Left unattended this will result in a blocked DPF, which can ultimately cause very expensive damage to other engine components. A blocked DPF is also potentially dangerous as it can cause overheating in the exhaust system and cause a fire risk. To prevent this damage most new vehicles will go into the “Limp Home” safety mode at this stage, meaning the vehicle will have minimum power barely sufficient to crawl home.
For regeneration to take place it requires the vehicle to be driven regularly at some speed on open roads e.g. motorway driving, typically driving at around 2500 RPM for approximately 15-30 minutes at least once a month. This should keep things working. Many diesel vehicles are used primarily in urban areas or for short stop start journeys e.g. local deliveries, taxi runs, school runs etc. and many have an auto gearbox, so the vehicle does not get the chance to heat up sufficiently and is unable to carry out a full regeneration process. Even if the regeneration functions as it should, over time the ash residue will build up in the DPF and have the same affect, ultimately resulting in a blocked DPF. For this reason a DPF is classified as a serviceable Item by the vehicle manufacturers like brake pads or air filters, and not covered under warranty. DPF systems therefore need to be maintained properly, or a solution found when they fail to work correctly.
What are my options?
If your DPF warning light or anti-pollution warning is on, please do not ignore it. Get professional advice, consider your options carefully and attend to the problem. Leaving it will ultimately cost you much more in additional repair bills and it can be dangerous.
By the time your DPF warning lights are visible your DPF will already be significantly blocked. Forced regeneration by a garage or a “blast down the motorway” is not likely to cure the problem. This will only work as preventative maintenance. At this stage realistically you only have two viable options, either replace it through an Original Equipment Manufacturer (OEM) DPF or have it removed and deleted.