DPF Frequently Asked Questions

A DPF is a ‘diesel particulate filter’ and is located within the exhaust system which helps reduce the harmful emissions that comes from a diesel exhaust. A DPF essentially captures and stores exhaust soot and when the engine gets hot enough it burns them off. Diesel particulate filters are thought to reduce soot emissions by as much as 80%.

A DPF has been a requirement of all new diesel cars since September 2009 when the Euro 5 standard came into operation in an attempt to reduce the emissions from exhausts. Some vehicles produced before this date also came with a fitted DPF.

Like any filter, if it is used repeatedly then there is a possibility it will become blocked and need emptying or cleaning. A DPF is equipped for ‘passive regeneration’, meaning that if you drive at a reasonably high speed in the motorway for around half an hour, this will allow the temperature of the exhaust to get high enough to burn off soot trapped in the filter.

The problem for many motorists is that their journeys often consist of short trips, or the engine is kept in low revs, so soot builds up to the point that the DPF gets blocked and the warning light on your dashboard comes on. If addressed early on it may be possible to clear it (consult your vehicle’s handbook) but it’s likely that you need to have it cleaned or replaced.

To cover scenarios where a motorist may not drive sufficient time for ‘passive regeneration’ to take place, vehicles are also equipped for ‘active regeneration’. This is where an the vehicle’s Engine Control Unit recognises that the soot has built up to a certain limit and then injects extra fuel in order to increase the temperature of the exhaust and burn off the soot in the DPF.

If passive or active regeneration fails to shift the soot and the DPF warning light remains, it is time to get the vehicle checked out on. Ignoring the issue can lead to a much more expensive fix than if you’d acted in the first instance. Some garages, including Edge Performance, offer DPF cleaning services and can usually remove the excess soot, allowing the DPF to work normally and regenerate again.

The key to keeping a DPF functioning effectively is to ensure that the regeneration cycle is able to work. To do this requires that you need to drive at a sustained speed for a period of time (consult your vehicle’s handbook). How often you need to do this will depend on the kind of driving you do, so if you are sitting in stop-start traffic most days, then it would be advisable to have a decent motorway run once a week to burn off the soot.

The most obvious sign of an issue with the filter system is the DPF warning light will illuminate on the dashboard. This can sometimes be accompanied by the engine management light, potentially highlighting a more serious problem. Other signs of a DPF problem include a loss of power or ‘limp mode’ being activated, a stuttering engine, a pungent smell of diesel, an increase in fuel consumption, and excessive smoke coming from an exhaust.

If your DPF warning light comes on, it will usually be safe for you to drive. Sometimes driving the vehicle at sufficient speed for a long enough period can be enough to clear the DPF of soot and the light may go out.

However, if you continue to drive the vehicle and ignore the DPF light, then there is a real possibility that you will see other warning lights come on, and the soot also will continue to build up. This could mean that the car will stop running properly and could become a risk because of its decreased performance levels. The longer you drive a vehicle with the DPF light on, the greater the risk of a very costly DPF replacement or worse.

At Edge Performance, a filter that is blocked due to an overaccumulation of soot can be removed and cleaned, allowing the vehicle to once again regenerate properly. This is usually the best and most cost-effective option, and preferable to replacing it with a brand new unit, which other garages might try to do. A replacement DPF unit could cost well in excess of £1,300, whereas cleaning it will cost around £180 to £400, depending on your vehicle.

From February 2014 all vehicles have to comply with legislation regarding emissions. It is not illegal to remove a DPF from a car or van, but they can not be used on public roads and can only be used off-road. The Road Vehicles (Construction and Use) Regulations (regulation) 61A(3)1 means that it is illegal to use a vehicle that has been modified in such a way that it no longer complies with the air pollutant emissions standards it was designed to meet. A missing DPF, where one was fitted previously, will result in an MOT failure.

DPF Frequently Asked Questions


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