A diesel particulate filter (DPF) captures soot produced when diesel burns, thereby preventing harmful particles from entering the atmosphere. This helps cut pollution and protect health, as soot from incomplete combustion is a major contributor to hazardous air quality.

While highly effective, DPFs need regular maintenance. They periodically burn off trapped particles in a process called regeneration. Otherwise, if regeneration is skipped or fails, the filter can clog, leading to reduced performance and costly repairs.

DPFs are used to help tackle the increase of global carbon emissions that come from more vehicles being on the road. The filter collects the soot to act as a barrier to these emissions and stops them from being released into the environment. This is why most modern cars come with a DPF included, especially since these filters are mandatory in all diesel motors. The soot needs to be cleaned off – but as we will discover why below, this does not 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.

Stop/start short journeys at low speeds are the main cause of blocked diesel particulate filters.  If a car spends most of its time being driven around town on short start-stop journeys, the exhaust doesn’t get up to temperature so the soot doesn’t get burnt off and the DPF does not ‘regenerate’ on its own. 

Other most common reasons for DPF failures include a clogged EGR Valve causing excess soot, faulty fuel injectors sending too much fuel to the air/fuel mixture, wrong type of engine oil, high mileage car will find regeneration harder, low fuel level – generally less than a quarter of a tank – will prevent regeneration taking place.

DPFs are designed to last in excess of 100,000 miles but if the drivers fail to operate the vehicle correctly, it will fail a lot earlier

If a DPF or engine management light stays on — especially alongside other indicators — act quickly to avoid costly damage. Delaying action can turn a simple fix into a major repair.

Forced regeneration might clear a blockage for a short time; however, the issue often returns within weeks. Without proper cleaning, the filter will clog again, causing smoke, reduced power, or limp mode. In some cases, the engine may even refuse to restart after a set mileage.

Driving with a blocked DPF can also damage other components, consequently leading to far more serious and expensive 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 that your DPF is clogged or notice the warning light appearing, then it’s essential to take immediate action. Instead of waiting for the issue to escalate, we provide a highly effective and affordable solution. As a result, using our state-of-the-art equipment, we offer on-the-spot roadside DPF cleaning, which helps you get back on the road quickly and efficiently.