Diesel particulate filter


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Understand your diesel particulate filter and the impact it has on your car’s performance and lifetime. Make up your own opinion after reading our articles.

What is a diesel particulate filter?


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A diesel particulate filter or also known as DPF is a component of the emission systems/exhaust system in modern diesel engines/cars. The diesel particle filter reduces the number of soot particles and fine dust inside the exhaust gases in order to meet the emission requirements.

During a periodic regeneration phase of the diesel particulate filter, the stored pollutants are converted into CO2 (carbon dioxide).

The exhaust gas stream is passed through a porous material inside the DPF, which consists of a tiny and fine honeycomb structure, according to the sieve principle. This cleans the exhaust gases of harmful particles. As a result, the filter reduces the proportion of soot particles by up to 90%.

Over time, many residues and dirt particles are collected inside the DPF. Therefore, the residues are burned at regular intervals during the “regeneration” to maintain the performance of the filter. During the journey, the engine control unit initiates the soot in the filter to be burned and become ash, while higher exhaust gas temperatures of approx. 600 degrees are present due to increased engine speed. This ash falls and remains at the bottom of the filter.

Regeneration can also be performed manually using the Carly “Diesel particulate filter” feature on BMW vehicles. In order to carry out the regeneration, however, some conditions must be met, such as no errors in the engine control unit or a functioning thermostat.

How long do diesel particulate filters last in vehicles?

No general answer can be given here, because it always depends strongly on how on the usage of the vehicle. In a vehicle that is driven a lot on the highway (long distance), a particulate filter can last up to 300,000 km. However, a DPF can also be defective after 150,000 – 200,000 km if the vehicle is often used for short trips.

However, the lifetime of the particulate filter can be increased. It is very important that the vehicle is always maintained and special engine oil for diesel vehicles is used. It is also important to fill up with quality fuel and to drive the vehicle frequently at a constant speed on the highway.

Nevertheless, a diesel particulate filter is also a wearing part that must be replaced at some point.

What happens if the diesel particulate filter is Full?

If the check engine light or the check light for the DPF comes on, the vehicle should first be read out to be able to check exactly which error is stored in the error memory.

If the error stored is about the diesel particulate filter is heavily loaded, one should not immediately panic.

On the one hand, you can try to start the regeneration manually with a brand-specific tester (also possible with BMW vehicles via the Carly app). If this is not successful, the DPF must be replaced.

It is important not to continue driving for a long time if the DPF indicator light is on, as this can cause damage to other systems, such as the turbocharger.

Components DPF system:

Filter element of the diesel particulate filter:

Depending on the manufacturer and make, the particulate filter is made of different materials, but normally, these materials are used:


-Silicon Carbide

-Aluminum titanate

-Sintered metal

The hot exhaust gases with the soot particles produced by the engine combustion are glided through the turbocharger directly into the diesel particulate filter. As soon as the exhaust gases flow into the DPF, they hit the various filter materials. Now the gaseous components in the exhaust gas flow through the very fine pores in the filter itself. The filter now absorbs and stores the harmful soot particles.

The load status of BMW vehicles can also be read out directly via the Carly app.

The differential pressure sensor of the diesel particulate filter:

The signal from the differential pressure sensor is very important for the engine control system because the engine control system uses the signal from the differential pressure sensor to decide whether to regenerate. The differential pressure sensor can measure the exhaust back pressure before and after the diesel particulate filter. If the measured back pressure is around 750 mbar (varies slightly from manufacturer to manufacturer), the engine control unit starts regeneration of the DPF.

Exhaust gas temperature sensor before and after the diesel particulate filter:

Exhaust gas temperature sensors are usually installed in gasoline and diesel engines. In diesel engines, the exhaust gas temperature sensor is not only responsible for monitoring the exhaust gas temperature but also to measure the temperature of the diesel particulate filter. It’s used in order to check whether the necessary temperature has been reached during regeneration.

Some vehicles have only one exhaust gas temperature sensor installed, but there are also vehicles that have this sensor installed before and after the DPF.

Cost of repair for a defective diesel particulate filters:

The evaluation of the repair cost is very difficult because first, you need to check exactly what is defective.

Even a defect of a sensor can give the impression that the diesel particulate filter is defective. A defective differential pressure sensor would be the cheapest part here (US$ 50 – 150). A new particulate filter can quickly cost several thousand dollars, considering the cost of repair including installation and removal if the filter itself is defective.

Very often the DPF can be cleaned professionally by specialized companies, and after cleaning the part is like new. In some cases, however, cleaning may no longer be possible. Thus, only a complete replacement of the diesel particulate filter will then help.

Diagnosis and repair of faults on the diesel particulate filter

If you suspect any issue, we recommend running a diagnosis using an OBD2 adapter, first. This will read your error memory from your ECUs. In many cases you can find out when an error (DTC) has been detected and what specifically the error is.

OBD adapters and diagnostic equipment can be used to diagnose a variety of engine problems, regardless of make or model. The issues found vary between simple sensor defects and more complex problems, such as turbocharger defects. In some specific cases, an OBD adapter can help fixing an issue. Sometimes just clearing old trouble codes (DTCs) will help, saving you a trip to the repair shop.

Whether you like fixing stuff yourself or you are a professional, a diagnostic device is a valuable tool that every driver should have in his car.

What should I do when the diesel particulate filter warning light is on, and how can I fix it?

If the diesel particulate filter warning light comes on, there is no need to panic immediately. In most cases, the warning lamp lights up due to a heavily loaded DPF, due to many short trips.

If the engine or exhaust system is not brought up to operating temperature due to frequent short trips, regeneration of the diesel particulate filter cannot take place.

Inferior engine oil or a dirty engine air filter can also be the reason for increased contamination of the diesel particulate filter.

To carry out the regeneration of the diesel particulate filter, the Carly app can be used to start regeneration on BMW vehicles.

Regeneration can also be initiated without special software. To do this, a predefined exhaust gas temperature must be reached (usually 600 degrees) and a constant speed (not below 40 km/h) must be maintained.

Of course, other errors can also cause the warning lamp to light up. For this, the error memory should be queried to see exactly which error is stored in the engine control unit.

Of course, this can also be done with the Carly app.

Keep in mind, that every car has different software and modules built-in. Therefore specific features will vary with every model.

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