Diesel Particulate Filter Cleaning - a step by step guide

Modern diesel vehicles are equipped with a Diesel Particulate Filter (DPF) to reduce harmful emissions. Their purpose is to collect the soot from the exhaust and prevent the harmful particles from being released and damaging the environment. While effective, DPFs can become blocked over time especially in vehicles that mainly do short journeys or urban driving.

Although they help protect the environment, if your fleet doesn't drive long distances, the DPF filters are at risk of being blocked. This is because the exhaust doesn't reach a hot enough temperature to burn the soot away.

Understanding how DPFs work, why they clog, and DPF Cleaning techniques can help you avoid costly repairs and keep your vehicle running efficiently.

What is a Diesel Particulate Filter (DPF)?

A Diesel Particulate Filter (DPF) is part of a vehicle’s exhaust system. Its job is to capture and store soot (particulate matter) produced during diesel combustion, preventing it from being released into the atmosphere.

Over time, this soot builds up inside the filter and must be burned off through a process called regeneration.

Types of DPF Regeneration

DPFs are designed to clean themselves through regeneration, but there are different types depending on driving conditions and vehicle systems.

Passive Regeneration

This happens naturally when the vehicle is driven at higher speeds (such as on motorways). The exhaust temperature becomes high enough to burn off soot automatically without driver intervention.

Active Regeneration

If passive regeneration doesn’t occur, the vehicle will trigger an automatic process. Extra fuel is injected to raise the exhaust temperature and burn off soot. This typically happens during normal driving but may require sustained speed.

Forced Regeneration

If the DPF becomes too blocked, a forced regeneration may be required. This is usually carried out by a mechanic using specialist diagnostic equipment, or sometimes manually by following a specific driving procedure.

Symptoms of a Blocked DPF

A blocked DPF often gives clear warning signs, including:

• A warning light appearing on the dashboard
• Reduced engine performance or limp mode
• Increased fuel consumption
• Difficulty accelerating
• Engine running hotter than usual

The most common sign is the DPF warning light, which indicates the filter is becoming clogged and needs attention.

What Causes a Diesel Particulate Filter Blockage?

DPF blockages are usually linked to how the vehicle is driven and maintained.

Short journeys and stop-start driving are a major cause, as the engine never gets hot enough for passive regeneration. Over time, soot accumulates faster than it can be burned off.

Other contributing factors include:

• Faulty sensors or EGR valves (Exhaust Gas Recirculation valve)
• Poor-quality fuel
• Excessive idling
• Engine issues causing incomplete combustion

Vehicles used mainly in urban environments are particularly prone to DPF problems.

Why Do DPFs Need Cleaning?

Even with regeneration systems, soot and ash gradually build up inside the filter. While soot can be burned off, ash (from engine oil and additives) cannot.

Without cleaning, this build-up can:

• Restrict exhaust flow
• Reduce engine efficiency
• Increase fuel consumption
• Lead to costly repairs or full DPF replacement

Regular cleaning helps maintain performance and extends the life of the filter.

Costs of Professional DPF Cleaning

Professional DPF cleaning is often the most effective solution for heavily blocked filters.

Typical UK costs:

• Basic cleaning: £100–£300
• Advanced off-vehicle cleaning: £250–£500

The price depends on the severity of the blockage and the cleaning method used. Compared to replacement, cleaning is usually far more cost-effective.

Costs of a New Diesel Particulate Filter

If a DPF is beyond repair, replacement can be expensive.

Typical costs:

• Standard vehicles: £1,000–£2,500
• Premium or specialist vehicles: £2,500+

This is why regular maintenance and early intervention are so important.

How to Clean a DPF Yourself – Step-by-Step Guide

If the blockage is not severe, you may be able to clean your DPF yourself using the following methods.

1. Heat the engine

The easiest and cheapest method of DPF filter cleaning is by driving the vehicle for a long-distance at high revs per minute. Doing this increases the heat of the exhaust and burns the soot blocking the DPF filter. It's best to drive on a motorway or A road where you can keep the vehicle at a consistent speed. If one of your fleet vehicles warning light comes on, the driver should continue driving, this will help clear the soot and will less likely require expensive maintenance care.

Drive at a steady speed (typically 40–60 mph) for 20–30 minutes in a lower gear to keep engine revs higher than normal.

Some vehicles may deal with the soot itself by injecting extra fuel to raise the temperature of the exhaust. This process is called 'active regeneration', which causes your vehicle's fuel economy to drop, and the engine noise to change. As the temperature of the exhaust heats up, it burns the soot away. However, this only happens if your car is moving and not stop-starting in traffic.

2. Use the recommended oil

Using the recommended manufactured oil can help with keeping the DPF filter clean. You should only use the specified oil as this will be specially made for your diesel vehicles. Once you have topped the engine with the correct oil, you will need to regularly check the oil level to make sure it doesn't run low.

3. Use premium fuel

You should consider asking your fleet drivers to only use premium fuel as it is claimed to burn more easily, keeping the DPF filter clear of any soot. Although premium fuel is more expensive, it will save your fleet from expensive garage costs to clear or replace the filter.

4. Don't ignore the warning light

The DPF warning light should not be ignored. If the light comes on, do not stop driving as this can make the blockage worse. Your driver should report the issue to their manager and continue driving to clear the soot until the warning light turns off. If this doesn't work, you will need to take the vehicle to a garage to have it professionally cleaned.

5. Regular servicing

To help with DPF filter cleaning, you will need to schedule regular servicing for your fleet vehicles. Services usually include an oil change by flushing out the existing oil and replacing it with new, clean oil which will help keep the DPF filter clean.

If your fleet only drives short distances in urban areas, you may find that your DPF filters are prone to blocking. You can try these DPF filter cleaning steps, but diesel vehicles generally perform better at long-distance driving. Using the wrong type of vehicle for your fleet can be expensive so from the outset you should consider and research the best vehicle for your fleet needs.

You will need to check the advice in the vehicle handbook for the recommended oil and fuel to get to most out of your fleet vehicles. Always be prepared for situations that can go wrong with your fleet and make sure your team has the relevant training to keep your fleet drivers and vehicles safe.

If the warning light remains on or the vehicle enters limp mode, a forced regeneration or professional cleaning may be required.

If you run a business with three or more vehicles check out our fleet insurance page for more information on protecting your fleet.

Maintenance and Prevention Tips

Preventing DPF issues is far easier and cheaper than fixing them.

Regular motorway driving is one of the simplest ways to keep your DPF clear. Even a 20–30 minute higher-speed drive every couple of weeks can make a big difference.

Using high-quality fuel and the correct engine oil also helps reduce soot and ash build-up. Keeping your engine well maintained ensures efficient combustion, which reduces the amount of particulate matter produced.

Avoid ignoring warning lights. Addressing issues early can prevent more serious (and expensive) problems later.

How Often Should You Clean Your DPF?

There’s no fixed interval for cleaning a DPF, as it depends heavily on how the vehicle is used.

As a general guide:

• Vehicles driven mainly on motorways may rarely need manual cleaning
• Urban or short-journey vehicles may need attention every 6–12 months
• Preventative driving (regular high-speed runs) can significantly extend intervals

If you frequently see warning lights or notice performance issues, it may be a sign that your driving pattern isn’t allowing proper regeneration.

Final Thoughts

A Diesel Particulate Filter is essential for reducing emissions, but it requires the right conditions to function properly. Understanding how it works and how to maintain it can save you from expensive repairs and keep your vehicle performing at its best.

By combining regular driving habits, preventative maintenance, and timely cleaning, you can extend the life of your DPF and avoid unnecessary costs.

DPF Cleaning – Frequently Asked Questions

How can I tell if my DPF needs cleaning?

The most obvious sign is the DPF warning light appearing on your dashboard. You may also notice reduced engine performance, higher fuel consumption, difficulty accelerating, or the vehicle going into “limp mode.” These are all indicators that the filter is becoming blocked and may need cleaning.

Is it ok to drive with the DPF light on?

It depends on the situation. If the light has just appeared, you can usually continue driving and attempt a regeneration (for example, a sustained higher-speed drive). However, ignoring the warning for too long can lead to a more severe blockage, potential engine damage, and costly repairs. If the light is flashing or accompanied by other warning lights, you should seek professional advice as soon as possible.

How long does it take to clear a diesel particulate filter?

A standard regeneration drive typically takes 20 to 30 minutes at a consistent speed with higher engine revs. If the blockage is more severe, it may take multiple attempts or require a forced regeneration or professional cleaning, which can take longer.

Can I clean a DPF myself?

Yes, in some cases. Light blockages can often be cleared by driving at higher speeds to trigger regeneration or by using a DPF cleaning additive. However, heavily blocked filters usually require professional cleaning or a forced regeneration using specialist equipment.

Can I pass an MOT with the DPF light on?

No, in most cases you will fail an MOT if the DPF warning light is illuminated. The DPF system must be functioning correctly, and warning lights related to emissions are considered a failure under MOT regulations.

Why is my DPF blocking up?

The most common cause is frequent short journeys or stop-start driving, which prevents the exhaust from reaching the temperature needed for regeneration. Other causes can include poor-quality fuel, excessive idling, engine faults, or issues with components like sensors or the Exhaust Gas Recirculation valve (EGR valve).

Is it illegal to remove the DPF?

Yes. Removing a DPF is illegal in the UK for vehicles that were originally fitted with one. It will also result in an MOT failure and could lead to fines. In addition, driving without a DPF increases emissions and may invalidate your insurance.

How can I prevent future DPF blockages?

Regular higher-speed driving (such as motorway journeys) is one of the best ways to prevent blockages, as it allows the filter to regenerate properly. Keeping your vehicle well maintained, using the correct oil and good-quality fuel, and addressing warning lights early will also help keep your DPF clear and functioning efficiently.