Diesel particulate filter: what is it ? how does it work ?

The automotive industry is faced with ever more rigorous environmental standards. The catalytic converter was brought in gasoline vehicles as early as 1993 and four years later for diesel cars. The Diesel Particulate Filter was first introduced in diesel cars before it was introduced in the exhaust system of gasoline-powered cars. But do you really know what this anti-pollution device consists of ? How does it work ? Does it require particular maintenance ? In this article, we will give you some answers and help to choose your new low-priced DPF.

What is the DPF ?

"The diesel particulate filter in my car is clogged", "I need to replace the DPF" are phrases that are frequently heard... But few motorists are aware of the real interest of the diesel particulate filter.

The diesel particulate filter became widespread on diesel vehicles from 2005 onwards. It consists of a metal cylinder present on the exhaust line, after the catalytic converter. Its role is to collect particles. These particles clump together until a regeneration cycle takes place. This means that when the vehicle is "hot", the DPF will inject fuel to ignite and destroy the particles. This reduces exhaust emissions. The catalytic converter, diesel particulate filter and EGR valve drastically reduce vehicle pollution. Moreover, the DPF is now generalized to trucks and other public transport. Even petrol cars, which were previously unaffected, are now equipped with this type of mechanical filter in order to obtain approval with the Euro 6.2 standard.

Did you know that ? The first production car to be equipped with a diesel particulate filter was the Peugeot 607 with the 2.2 HDI engine.

Maintaining a DPF

Gasoline and diesel vehicles are unhoused under the same roof. Unlike gasoline engines, diesel engines have a risk of clogging. This is mainly the case for those used mainly in cities. For regeneration cycles to take place, it is therefore necessary to clean the DPF while driving as much as possible. However, not all filters are the same. The monoliths lining the interior can be of quite a variable quality. This means that some DPFs will retain particles less well and have a shorter life. Therefore, we recommend stainless steel diesel particle filters. These do not rust and often have a ceramic interior. A quality DPF (Which is not necessarily the most expensive !) does not require any maintenance apart from regular regeneration cycles. As for descaling, which is promoted by many professionals, we do not recommend it because of the damage it can create in the medium and long term.

Why is this part necessary ?

The road transport sector in all its forms is one of the activities that generate important air pollution. This pollution comes, among other things, from the fine particles emitted by vehicles with thermal engines. These particles (Particulate Matter or PM) are extremely small, with a diameter of less than 2.5 µm (microns)*. But the smaller the size then the more harmful they are. The PM infiltrate the airways and in the long term cause or aggravate respiratory diseases: asthma, bronchitis, cardio-pulmonary pathologies.

The diesel has always been criticized for its excessive release of fine particles into the air, due in particular to incomplete combustion of fuel. A recent study - cited by Le Figaro in an article dated 16 December 2020 - by the French Institute of Petroleum and new energies (Ifpen) shows however that for equivalent models, some diesel vehicles pollute less than petrol. This is likely to rekindle a debate that has never really been extinguished in France…

*1 µm (micrometer) corresponds to one thousandth of a millimeter.

How it works

So how does it work, to use the favourite expression of a well-known French scientific journalist ? In principle it is quite simple, but make no mistake, the diesel particulate filter is a sophisticated technology, that is constantly evolving.

If you are looking for the location of the diesel particulate filter, it is easy to find. It is a metal cylinder in the exhaust line, after the catalytic converter. Inside this cylindrical tube is a honeycomb structure through which the exhaust gases flow.

The filter traps and collects the fine particles. These particles clump together to a certain extent and are then burned off. This is known as regeneration. When the vehicle is « hot », the DPF injects fuel to ignite and destroy the particles. This lowers exhaust emissions.

The catalytic converter, the diesel particulate filter and the EGR valve make it possible to drastically reduce vehicle pollution. Moreover, the DPF is now widely used in trucks and other public transport. Even the petrol cars, which have been spared until now, are now equipped with this type of mechanical filter, in order to obtain homologation with the standard Euro 6.2.

How do I know if my car is equipped with a DPF ?

The diesel particulate filter became mandatory in 2011, for new diesel vehicles. However, some manufacturers were able to equip certain models well before this, as this anti-pollution device became widespread from 2005. The Peugeot 607 2.2 HDI engine is the first production car to be fitted with a DPF.

If you buy a new car, the problem does not arise. It becomes more difficult when you buy a used car, especially from a private person. Many motorists do not see the DPF as a device to make cars more environmentally friendly. Instead, they see it as an extra part to maintain, which reduces the performance of their car and increases the bill at the garage when it comes time to change it. Or when the honeycomb becomes a nest of problems.

Removing the DPF from a car is prohibited. If you buy a car that has been stripped of its filter, you will be in trouble (for example failing the roadworthiness test) and have no recourse against the seller. But, it is difficult to know precisely whether the filter has been neutralised, even by crawling under the vehicle. So how can you be sure that you are not being cheated ? Jean Savary, in a post on the Caradisiac website, advises the following: « Never buy a second-hand diesel without being certain that it has not been tampered with. There's only one way to find out [...] run the car you want through a 5 gaz analyser. Many car centres are now equipped with them, as are most dealerships and already some test centres of CT ».

How to prevent a diesel particulate filter from clogging ?

« My car's diesel particulate filter is clogged », «  I need to replace the DPF » phrases that are frequently heard... But few motorists know the real benefit of the diesel particulate filter. Petrol and diesel vehicles are not in the same boat. Unlike petrol engines, diesels have a risk of clogging. This is mainly the case for those used mainly in the city. The increase in short urban journeys at low speed prevents the engine from reaching the optimum temperature for the regeneration cycles to be triggered.

It is therefore necessary to clean the DPF while driving as much as possible. The method is very simple, just drive regularly at a certain engine speed. You will effectively clean your part and prevent it from becoming clogged. If you don't drive much or mostly in the city, schedule a short trip on the motorway every month, you will certainly extend the life of your part.

When should I change my DPF ?

The life of a diesel particulate filter depends very much on your driving style and habits. Nevertheless the averages are between 80 000 and 120 000 km, but the range is still quite wide.

Among the lhts on your dashboard, there is one dedicated to checking the correct operation of the diesel particulate filter. If it lights up, you should not ignore it and look for the cause of its appearance. If you are in doubt, a quick look in your vehicle's technical manual will definitely enlighten you as to what to do.

How to choose the right DPF ?

Not all filters are created equal. The monoliths that line the interior can vary in quality. This means that some DPF will retain fine particles less well and have a shorter life. Therefore, we advise you to the stainless steel diesel particulate filters. These do not rust and often have a ceramic interior. A quality DPF (which is not necessarily the most expensive one, just browse our site to see !) does not require any maintenance apart from regular regeneration cycles.

As for descaling, promoted by many professionals, we do not recommend it, because of the damage it can cause to the engine in the medium and long term.

How to remove a diesel particulate filter ?

Loss of power, a warning light, a stalled engine, choking, or a shift to a lowered mode are all signs that a diesel particulate filter needs replacing. In this case, it is better not to wait too long, because driving with a damaged DPF can seriously damage the engine.

Comment remove a diesel particulate filter ? the replacement of the DPF is an operation that requires some mechanical knowledge, good tools and a suitable working infrastructure. That's why we've dedicated an entire article to this type of repair and you should know that our parts all come with assembly instructions. Of course, you will need the right part. Krosfou offers Quality DPFs at low price. 

Did you know ? At Krosfou, we make our own diesel particulate filters, in stainless steel and ceramic coating. Our objective : to offer you quality equipment at prices well below those usually charged.

How much does it cost to change a DPF ?

How much does it cost to change a diesel particulate filter ? As you can imagine this depends on the model of your vehicle. The range is between 1 000 and £1 500, including parts and labour. For a Citroën C4, the average is around £1 000 (according to the website vroomly.fr) and £900 for a Peugeot 307. If you have a BMW serie 1, you should expect to pay up to £1 500. Please, note that these are only averages, so whatever your vehicle, replacing this part is far from trivial on a budget. It is therefore advisable to ask for several estimates and to choose carefully who you entrust with this repair.

If you decide to change the part by yourself, you can considerably reduce the cost. For example, Krosfou offers DPF for the Citroën C4 or Peugeot 307 at prices ranging from 227 to £536. Such a price difference does not leave anyone indifferent !

Remove the DPF ?

If you go on the forums, many « experts » boast of having removed the DPF of their vehicle. In their opinion, the latter is useless and removing it allows the vehicle to breathe. Technically, this is feasible. Legally, it is forbidden and we advise you not to be tempted by this kind of practice. Until a few years ago, some garages even listed this « skill » among their services. In addition to removing the part, the engine control unit was reprogrammed and the EGR valve deactivated. All of this in compliance with the manufacturer's standards and with a guaranteed passage at the technical inspection. It's like a dream.

If you remove the diesel particulate filter from your vehicle, you risk a fine of up to £7 500. Before that, you will certainly fail the technical inspection, which has become much stricter since 1^er January 2019.

A question, a doubt about the choice of a diesel particulate filter for your car ? Call on Krosfou, the European specialist in stainless steel DPF. We put our expertise at your service, in less than 24 h, at your home or in a relay point. Don't wait any longer and choose a premium service, at factory price.

Do you want to know if your Catalytic Converter is Bad ? Do you want to know if your DPF is clogged ?

Replacing a DPF : How to do it ?

Loss of power, display of an engine light, engine stalling, choking, switching to degraded mode; these represent all signs that can indicate that a diesel particulate filter need to be replaced. In this case, it is better not to wait for a long time because driving with a damaged DPF can seriously damage the engine. Replacing the DPF is fairly simple as long as you have a few tools at your disposal. All you have to do is to find a quality DPF at a low price by looking for the reference number corresponding to your car. Did you know that ? At Krosfou, we make our own diesel particulate filters, in stainless steel and ceramic coating. Our objective: to offer you quality equipment at prices well below those usually practiced.