DPF Specialist FAQ

A diesel particulate filter (DPF) captures soot generated during diesel combustion, preventing harmful particles from polluting the atmosphere.

Soot and other particulates form when diesel fuel doesn’t burn completely. These emissions contribute significantly to air pollution and pose serious health risks.

While particulate filters effectively reduce diesel emissions, they must regularly burn off trapped soot in a process called regeneration.

To explore more tips on diesel vehicle care, visit Auto Assist Group.

DPFs help reduce global carbon emissions caused by the growing number of vehicles on the road. These filters collect soot and act as a barrier, preventing harmful emissions from entering the environment. That’s why most modern cars include a DPF—especially since regulations now require all diesel engines to have one. You need to clean the soot regularly, but as you’ll see below, that doesn’t always happen.

A DPF can hold a certain amount of soot, but not a huge quantity, so it needs to regularly go through a process of regeneration in order to clear out the soot and allow the vehicle to operate correctly. Regeneration occurs when the filter reaches a sufficiently high temperature, allowing the soot to be converted to a much smaller amount of ash.

To allow the DPF to automatically regenerate, the engine should be used regularly at a sufficient speed, to ensure a high enough temperature of the exhaust gas is reached. Although it may vary from manufacturer to manufacturer, typically a vehicle must be driven at 50mph or above for at least 20 minutes in order to automatically regenerate the filter. During the regeneration phase, high temperatures in the filter may cause a slight smell, especially during the first regeneration.

Frequent short stop/start journeys at low speeds are the leading cause of blocked diesel particulate filters (DPFs). When drivers mostly use their vehicles for short city trips, the exhaust system doesn’t reach a high enough temperature to burn off soot. As a result, the DPF cannot regenerate properly.

Other common causes of DPF failure include a clogged EGR valve, which leads to excess soot; faulty fuel injectors that disrupt the air/fuel mixture; using the wrong type of engine oil; and driving a high-mileage vehicle, which makes regeneration more difficult. Although manufacturers build DPFs to last over 100,000 miles, improper vehicle operation can cause them to fail much sooner.

If your warning light continues to stay on, turns red, or additional DPF lights come on, do not leave it too long before getting it checked by a specialist.

More damage can be caused this way and what could be an inexpensive fix can become something much more expensive.

Some garages can clean blocked DPFs, in a process called forced regeneration but this is found to be a temporary fix and just masks the problem for a period of 2-4 weeks and the same issue will occur again.  Failure to correctly fix the issue that is the cause of most diesel particulate filter issues: they become blocked more and more which increases exhaust emissions, stifles engine performance and sometimes even puts the car into a restricted ‘limp-home mode’. On some models the engine may not restart after a number of miles, constantly driving with a blocked DPF can cause further damage to components causing real problems

When you see a flashing DPF warning light, you may consider removing it to solving the problem. This is not a great move for the planet and is, as mentioned, illegal in some places. Moreover, as of recently, cars that have had their DPFs removed will fail their MOT. It can be done, and you will find companies offering this service online, but it is just not worth it. It can even invalidate your motor insurance.

Diesel particulate filters are very expensive. A new one from a car manufacturer can cost £1,000 and £3,500, plus any diagnostic or labour charges, There are now other suppliers of diesel particulate filters that charge less, but be careful as they must still have the correct Type Approval or they may not work correctly and end up costing you more in repairs leaving you again with high repair bills.

It is natural that your DPF will become clogged, especially if you do not make frequent long-distance journeys. However, there are ways of helping your DPF stay clean. You need to make sure you use the right type of oil. Choose oil which is low SAPS. The fewer number of sulphate ash particles the less chance of your DPF clogging up. The second way to keep your DPF clean is to get a professional DPF cleaning company to take a look at your DPF at regular intervals.

If you suspect your DPF s clogged or you have seen your DPF warning light, then you need to act.  

With our state-of-the-art equipment, we offer roadside DPF cleaning to get you on your way again, fast. Whether it be a van, a car or a lorry, our specialist equipment is capable of identifying your DPF’s performance and bringing its levels of soot and matter back down to an immaculate clean. We can even provide you with the before and after results to show you our work that has saved you money in the long term.