The transmission filter has to be replaced

Diesel particulate filters: you need to know that

All diesel vehicles have had particulate filters for a long time. They ensure that diesel engines do not form soot. We answer the most important questions about this cleaning system: How does the filter ensure clean exhaust gases? When does it have to be replaced? And can it also be cleaned inexpensively?

  • The soot particles must be burned in the filter at more than 550 degrees

  • A particle filter doesn't last forever. Exchange costs: between 1000 and 2000 euros

  • Cleaning instead of replacement: the car manufacturers are skeptical

What does a particle filter do?

Particle filters are able tofilter out more than 90 percent of the sootand burn them - including many fine particles that are suspected of causing cancer.

The models built in series are usually so-called closed wall-flow filters. The diesel exhaust gases are through aporous filter wall made of ceramic or metal. The attraction of the molecules of different substances (adhesion) holds the soot particles in the exhaust gas to the wall. These collect on the inside of the filter.

Because more and more particles accumulate in the filter over time, they are burned off regularly. For this, the exhaust gas temperature must be above the soot ignition temperature of 550 degrees Celsius. With this as"Regeneration" This process mainly produces carbon dioxide (CO₂) and water vapor. A small residue remains in the filter as ash.

This is how regeneration works

The regeneration of the particle filter depends on the system used, which differs from manufacturer to manufacturer. A distinction is made between active and passive regeneration. Usually both options are combined.

  • Passive regeneration: It takes place continuously and always when the required exhaust gas temperature is reached by itself. This is especially the case with predominantly motorway or full load operation.

  • Active regeneration: It is initiated by increasing the exhaust gas temperature to around 600 degrees Celsius and by changing the number and timing of the injections, sometimes also by increasing the load (e.g. switching on large power consumers). This is necessary if the car is frequently operated with a lower load (e.g. in city traffic).

There are also soot filters in which an additive in the diesel fuel lowers the soot ignition temperature and enables the particles to be burned from around 400 degrees. Disadvantage: The additives burn in the engine and there is also ash in the filter.

The limits of regeneration

Longer short-haul operation can impair the regeneration of the particulate filter because the exhaust gas temperature does not reach the required temperature. The result: the filter clogs or is damaged.

To avoid this, the lights upParticulate filter indicator light in the dashboardon when the soot load has reached a certain limit. Then a look at the operating instructions helps and a so-called "regeneration drive" with increased load (e.g. higher speed on the motorway) according to the manufacturer's specifications is usually to be carried out. There is also the possibility of an emergency regeneration in the specialist workshop if regeneration is no longer possible during normal driving.

Once a certain ash load limit has been reached, the filter cannot be regenerated in the workshop either. TheThe particle filter must then be replaced.

By the way: residues of engine oil also cause residues in the particle filter, which can no longer be removed by regeneration. It is therefore particularly important to refer to the one prescribed by the manufacturerOil quality with so-called "low-ash properties"to pay attention to.

When does the particle filter have to be replaced?

Even with correct regenerationthe filter asserts itselfash toand requires an exchange. The regeneration intervals become shorter until the control lamp finally indicates that regeneration is no longer possible and the engine goes into limp-home mode. If the particle filter is clogged by the ash, the initiation of a filter regeneration by the workshop is no longer successful. In this casethe particle filter must be replaced. Its service life depends, among other things, on the driving style, the area of ​​application, the mileage and the engine oil.

Some older models haveconcrete intervalsspecified for replacing the particulate filter - usually between 120,000 km and 180,000 km. It is now more common to make the replacement of the particulate filter dependent on its ash content. This is determined by the workshops during the inspection.

The installation of a new particle filter costs depending on the modelbetween 1000 and 2000 euros. Some vehicle manufacturers also offer cheaper replacement filters as part of their own exchange programs.

ADAC Ecotest: How environmentally friendly are our cars?

BlueMotion, Efficient Dynamics, BlueHDi - the manufacturers come up with marketing terms that are all supposed to suggest how clean their cars are.

However, you should not rely on it. This is shown by the ADAC Ecotest, which the club carries out on every test car. CO₂ and pollutant emissions are determined under realistic conditions and the result is summarized in a star rating. Quite a few alleged cleaners turn out to be a dirt thrower in reality.

Here you will find all current models in the ADAC Ecotest

Cleaning instead of replacement: does it work?

Can a filter also be cleaned instead of replaced? Various companies offer exactly that. As a rule, these are mechanical or thermal processes or a combination thereof. Theexact cleaning processThe respective providers do not reveal, but promise that the flow behavior of the filter can be compared with that of a new part. However, the companies make no statement as to how long the catalytic coating will remain effective afterwards - no one mentions a "minimum duration".

A particle filter cleaning costs around 400 to 500 euros. It should be noted that the particle filter is removed and ready for cleaningmust be sent to the provider. The vehicle can therefore not be used for a few days.

In addition to the above cleaning methods arealso chemical cleaning agents to have. These are intended to remove the soot particles that have remained in the filter if regeneration is incomplete or interrupted. But you cannot remove any ash deposits. The same also applies to additives that are added to the fuel and are intended to keep the load on the particle filter low or to clean the filter.

Automakers don't recommend cleaning

When asked by the ADAC, no car manufacturer recommends the cleaning methods or agents described. Also the use of additives isnot approved by any automaker.

Damage occursthat can be traced back to filter cleaning or the use of additives, the manufacturer or seller is therefore not responsible for this within the scope of the vehicle guarantee or liability for material defects. This also applies to consequential damage and irregularities resulting therefrom.

What is the ADAC's position on this? Unfortunately, it is not possible to check how good the cleaning methods actually are. A representative consumer protection test by the ADAC is not possible because different cleaning methods are used (partly company secret), the soiling of the filters differs greatly and the design of the filters varies depending on the vehicle type (e.g. size, material, coating). A general statement would therefore not be possible in a test.

Conclusion:The ADAC experts can for the reasons mentioned aboveno general recommendation for the particle filter cleaning processes and cleaning agents offered on the market.

The particulate filter should not be confused with an SCR catalytic converter with Ad-Blue injection. The latter cleans the diesel exhaust gases from the currently much discussed nitrogen oxides. Here you can readhow an SCR-Kat works.

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