Diesel versions, such as the Ford Mondeo, regularly suffer from a blocked particulate filter. This leads to loss of power, higher fuel consumption and a warning light on the dashboard. If you ignore the problem, the car will emit black smoke and a strong smell. Read on for recognisable symptoms and concrete solutions.
What does a particulate filter do?
The particulate filter, also known as a DPF (Diesel Particulate Filter), has been mandatory for all new diesel models in Europe since 2011. The filter captures harmful soot particles in a porous ceramic structure with a honeycomb pattern. These particles are then burnt off during the regeneration process, being converted into harmless gases.
This regeneration process starts automatically when the filter becomes full. The engine increases the exhaust gas temperature to at least 550°C to burn off the soot. In normal use you will not notice this. The system manages everything itself.
‘ Replacement is then the only option, because since 2017 removing particulate filters has been legally prohibited in Europe. ’
How long does a particulate filter last?
A particulate filter does not last forever. For diesel versions the service life is roughly 150,000 to 200,000 kilometres. After this distance the filter gradually becomes blocked and can fail. Replacement is then the only option, because since 2017 removing particulate filters has been legally prohibited in Europe.
How do I know if my particulate filter is blocked
A blocked particulate filter gives off various warning signals. The earlier you recognise them, the better you can prevent costly repairs.
The DPF warning light is on
This is the clearest sign. The light appears on the dashboard when the regeneration process has failed or the soot build-up has reached a critical level. Never ignore this light.
Loss of power and slow response
A blocked filter restricts the exhaust gas flow. This creates back pressure on the engine, causing the vehicle to deliver noticeably less power. The car feels heavy and responds sluggishly to the accelerator pedal.
Increased fuel consumption
Due to the extra back pressure, the engine has to work harder. This results in significantly higher fuel consumption, which you will quickly notice when refuelling.
Black or grey smoke from the exhaust
A properly functioning particulate filter ensures an almost invisible exhaust. Dark smoke indicates that the filter is overloaded and can no longer keep up with the amount of soot being produced.
Hard starting and irregular running
The back pressure disrupts the combustion process. This can lead to starting problems, vibrations or an irregular, howling sound when the engine is idling.
Why does the regeneration process fail
Regeneration fails under certain conditions. These are the most common causes:
Short trips and city traffic
This is the main cause of particulate filter blockage. Drivers who mainly do short journeys and do not exceed 3,000 rpm never reach the required combustion temperature of 550°C. The soot builds up without being burnt off.
Incorrect oil or fuel
Inferior products significantly increase soot formation. Always use low-SAPS oil (oil with low ash and sulphur content, suitable for engines with a particulate filter), which is specially developed for diesel engines with particulate filters. When this oil is burnt, less ash is produced.
Defective components
Sensors, the EGR valve (a valve that routes part of the exhaust gases back to the engine) or fuel injectors (the nozzles that inject fuel into the cylinders) affect the combustion process when they are not working properly. If these components malfunction, excessive soot deposits will form.
Deferred maintenance
Ignoring regular oil changes and filter checks accelerates blockage. Old oil contains more contaminants that produce extra soot.
‘ As the blockage increases, the pressure difference rises and the engine initiates a regeneration. ’
How does the system detect a blockage
Many diesel engines have a differential pressure sensor (a sensor that measures the pressure difference before and after the particulate filter) positioned before and after the particulate filter. This sensor measures the pressure difference and determines how much soot is in the filter. A clean filter shows a minimal pressure difference. As the blockage increases, the pressure difference rises and the engine initiates a regeneration.
Temperature increase for regeneration
Soot only burns at around 550°C, a temperature that is not normally reached in the exhaust system. Manufacturers therefore use different strategies:
- Eolys additive: Some brands add a fluid called Eolys (a special additive that lowers the combustion temperature of soot) to the fuel via a separate reservoir. This cerium-based additive lowers the combustion temperature of soot to 450°C.
- Extra diesel injection: Other manufacturers inject additional diesel fuel into the system, raising the temperature in the filter to 650°C so that the soot is actually burnt off.
Can I clean the particulate filter myself
There are several ways to tackle a blocked particulate filter. Some you can do yourself, others require professional help.
Passive regeneration
This is the simplest method. Drive for at least 30 to 45 minutes on the motorway at a speed above 65 kilometres per hour and keep the engine speed above 3,000 rpm. The engine will then become hot enough to burn off soot particles automatically.
Manual regeneration
Many vehicles offer the option to start a manual regeneration via the on-board menu. This raises the engine temperature and can help prevent blockages. Check your car’s manual for the specific procedure.
Forced regeneration at a garage
In the case of a more serious blockage, a garage can carry out a forced regeneration. This is done with specialist equipment that runs the engine very hot under controlled conditions.
Chemical cleaning agents
For stubborn blockages there are cleaning additives available for the particulate filter (DPF). You can add these products via the fuel tank system. They help dissolve deposits in the filter. Note: this only works for light to moderate blockage.
Professional cleaning or replacement
When the filter can no longer be saved, it must be cleaned or replaced by a specialist. A specialist can remove the filter and clean it mechanically using special equipment.
‘ Professional cleaning usually costs between 200 and 400 euros and in many cases can prevent replacement. ’
How much does it cost to replace a particulate filter?
The cost of replacing a particulate filter is between 500 and 1,500 euros, depending on the make, model and whether you choose an original or aftermarket part. Professional cleaning usually costs between 200 and 400 euros and in many cases can prevent replacement.
Practical tips to prevent blockage
With the right maintenance and driving style you can prevent many particulate filter problems.
- Plan regular longer journeys: Drive a longer journey on the motorway at least once a month. This gives the regeneration process the chance to run to completion.
- Use the correct oil: Always use low-SAPS oil and replace it according to the prescribed maintenance schedule. This reduces excessive soot formation.
- Fill up at reliable stations: Use high-quality fuel to minimise contamination.
- Deal with warnings immediately: If the DPF light comes on, act straight away. Early intervention prevents costly repairs.
- Check other components: Have injectors, turbo seals and the EGR valve checked regularly. Defective components increase soot production.
- Avoid continuing with a blocked filter: Continuing to drive with a completely blocked filter damages the engine and can lead to expensive repairs.
What you need to remember about particulate filter blockage
Particulate filter blockage is a common problem with diesel vehicles, especially for drivers who mainly make short journeys. The symptoms are easy to recognise: a warning light, loss of power, higher fuel consumption and smoke. Early recognition and action are important to prevent engine damage and high repair costs.
Regular maintenance, using the right oil and planning longer journeys prevent many problems. Plan at least one motorway trip of 30 to 45 minutes each month. This keeps the particulate filter clean and prevents costly repairs. Does the DPF light come on anyway? Then immediately try a passive regeneration by taking a longer drive. If this does not help within a week, contact a specialist for a forced regeneration or professional cleaning.
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Frequently asked questions
The most common causes of a particulate filter blockage are lots of short trips that do not get the filter hot enough to regenerate, poor fuel or oil quality, defective sensors or EGR valve, and postponed maintenance or other engine problems (e.g. injectors, turbo). You can prevent this by regularly making longer motorway journeys so the regeneration process can do its job, always using the prescribed low-SAPS engine oil and good-quality fuel, and strictly following the maintenance schedule. If any warning lights come on or you notice loss of power, have a diagnosis carried out immediately so that a forced regeneration or repair can take place in time.
Symptoms of a blocked particulate filter include a DPF warning light on the dashboard, reduced engine power, higher fuel consumption and sometimes dark smoke from the exhaust, or an engine that runs poorly and will not rev high. If you recognise these signs, do not keep driving for too long but preferably take a longer trip on the motorway to give regeneration a chance. If the light stays on or the car continues to perform poorly, go to a garage as soon as possible for diagnosis and (possibly forced) regeneration. Do not ignore these issues, as they can lead to expensive damage to the particulate filter and engine.
A blocked particulate filter can sometimes be resolved by (passive or forced) regeneration or by using chemical cleaning agents; the advantage is that this is relatively inexpensive and the original filter is retained, but it does not always work with severe or persistent blockage. Professional removal and cleaning (by a specialist) is more thorough and can significantly extend the filter’s service life, but it costs more time and money and is not always successful with an older or damaged filter. Replacing the particulate filter is the most definitive solution and restores flow and emissions to as-new condition, but it is by far the most expensive option. Removing the particulate filter is illegal and will lead to MOT failure and possible fines.
A blocked particulate filter causes extra back pressure in the exhaust, so your engine loses power, uses more fuel and eventually runs worse or becomes hard to start. Driving like this for a long time can lead to engine overheating, damage to the turbo, EGR system and sensors, and therefore expensive repairs. The filter itself can also become so damaged that it has to be completely replaced, which costs hundreds or even thousands of euros. You also risk failing the MOT and getting fines if the particulate filter no longer functions properly.