A DPF (Diesel Particulate Filter) 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.
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 newer vehicles will go into “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 approx 30mins at least once a month, this will keep things working. However, many diesel vehicles are used primarily in urban areas or on short stop start journeys e.g. local deliveries, taxi’s, school runs etc and many have 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 etc and not covered under warranty. DPF systems therefore need to be maintained properly.

If your DPF warning light  is on, please do not ignore it (typical dash warning symbols below). 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, these only work as preventative maintenance. So at this stage realistically you have the following 2 options:-

DPF Removal
DPF Replacment

It is not illegal to remove the DPF, however in the UK it is an offence to use a vehicle on the road that no longer complies with the emissions standards it was designed to meet.
Changing any part of the exhaust or emissions system with a part other than the vehicle manufacturer’s original part that may change the emissions could be an offence. Currently emissions testing outside the London Emissions Zone (LEZ) is limited to the standard MOT test.