Diesel Particulate Filter Problems: Replace, Clean or Delete?

Tired of the problems caused by FAP diesel particulate filters, especially in diesel engines, or because of how expensive it is to replace a filter when it fails -around 2,000 euros, depending on the vehicle and engine-, more and more drivers are considering having it cleaned by a specialised workshop, while others still choose to remove it entirely.

The first thing to say is that driving a car with the particulate filter removed is illegal, as well as harmful to the environment. It is also important to know that the best way to avoid particulate filter failures, besides taking a few very simple measures, is to clean it yourself… by driving. Here we explain how to avoid particulate filter failures: 10 tips to make your diesel car’s particulate filter last longer.

What is the particulate filter for?

To better understand why particulate filters fail and the problems and faults they cause, it is best to know how they work, at least briefly. The FAP reduces a specific type of emission: the solid particles generated during combustion. There are particulate filters for petrol engines and for turbodiesel engines. The ones that cause the most problems, due to the characteristics of the fuel and this type of engine, are diesel particulate filters, as they generate the most particles during combustion.

These filters, which are fitted in the exhaust system, have a ceramic material structure inside them forming a series of channels in which the harmful particles travelling in the exhaust gas flow are trapped as they pass through the filter. To remove these particles before they clog the filter, AdBlue is normally used, an additive that lowers the temperature at which these particles burn off, facilitating the passive regeneration of the filter process. The first particulate filters did not need AdBlue, but there are practically none left; they are only found on older cars.

If this is not enough, which it normally is not -it depends greatly on the conditions of use of the car and the driving style-, the filter may require active regeneration. This is a process that starts automatically when the system detects a certain pressure differential between the inlet and outlet of the exhaust gases at the filter, due to the build-up of these harmful particles. For this process to occur, the system carries out additional fuel injections while the engine is running, which raise the temperature of the exhaust gases and help clean the particulate filter.

Why does the particulate filter fail?

As you can imagine, stopping the engine while it is performing an active regeneration process, which can last several minutes, is not good for the FAP. The problem is that there is no way to know whether the filter is regenerating, as no warning light comes on in the instrument cluster.

On short trips or when driving mostly in town, besides generating more particles, it is easy to interrupt a regeneration process… or even several in a row, causing the filter to clog. A possible solution in these cases is to go to the workshop and have them carry out a forced regeneration: the engine is “forced” to complete an active regeneration process using the diagnostic machine.

The filter may also stop working because it has reached the end of its service life. In this case, regeneration cycles are no longer possible; the filter has simply lost its ability to “trap” particles and remove them through these regeneration processes.

How do I know if the particulate filter is clogged and what should I do?

Some vehicles have a specific particulate filter fault warning light, which comes on in the instrument cluster when there is a problem. In other cases the same engine fault light comes on, which can indicate other problems related to the engine’s injection or emissions control systems, for example the EGR or the mass airflow meter.

A clogged FAP, or one that is not performing its function, can cause anything from increased fuel consumption to loss of power, difficulty for the engine to rev up, or even activation of the emergency operating mode. The final diagnosis is normally made at the workshop, with the right equipment.

Once a problem with the particulate filter has been identified, there are basically two solutions: replace it or try to clean and/or rebuild the faulty filter. The most effective is the first, but also the most expensive: replacing the particulate filter with a new one can cost between 1,500 and 3,000 euros depending on the vehicle, compared with around 300 euros for a cleaning.

For our part, we do not consider the option some users choose as a third solution, whether because cleaning is not possible -the filter has reached the end of its service life and should be replaced- or simply to forget about regeneration problems, whether the car is used on short or long trips, or having to top up AdBlue. We are referring to removing or deleting the particulate filter, something completely illegal. We will discuss this later.

Cleaning the particulate filter

There are different ways to clean a clogged particulate filter.

Additives added to the fuel

And here I would like to start by talking about additives that are added directly to the fuel tank, such as these from Motul or from LIQUI MOLY. These additives are normally not for cleaning the filter, but to help prevent it from clogging when used regularly.

It is an affordable solution, around 15 euros per bottle, which does not require a visit to the workshop, although its effectiveness is rather low. They may work in cases of partial filter blockage; in fact, there are reports from users who have had success. However, check the type of product and its compatibility first. Some are not suitable for engines that already have an SCR system with AdBlue, while others are suitable for all types of engine. Are there risks? Yes: although unlikely, there is a possibility of damaging the ceramic internal structure of the filter, due to the chemical aggressiveness of the additive.

Professional FAP cleaning at the workshop

There are different methods. One of them is spraying with a high-pressure gun (pressure washer) using a specific product that removes the dirt embedded in the filter, followed by a rinsing process. This may not require removing the filter, but it is dangerous: if it is located very close to the engine, liquid can enter the combustion chamber, for example through an open exhaust valve. It is a relatively effective process.

Another somewhat more effective system, and very popular at present, is cleaning the particulate filter using ultrasound. This process dislodges the dirt adhered to the walls of the ceramic component of the filter by applying ultrasound. Newly designed ultrasonic machines work by submerging the filter in a tank containing cleaning liquid, then applying ultrasound at a suitable frequency so the dirt softens and comes loose.

https://www.youtube.com/watch?v=2_Hp5DCyiW0

However, the best results are achieved with special FAP cleaning machines or booths. These machines inject water and a special detergent additive, with the advantage that they flow in both directions, ensuring effective cleaning and, very importantly, complete drying after the process.

The cost of cleaning a particulate filter at the workshop can range between 200 and 400 euros.

Removing the particulate filter

And we come to the most delicate issue, the removal or deletion of the particulate filter. Let us repeat, so there is no doubt, that this is a completely illegal practice, which fortunately is no longer as popular, but which many users still resort to when cleaning or repair is not possible, or they cannot afford to buy and fit a new filter. How much does it cost to delete a particulate filter? Well, do not think it is cheap… depending on the vehicle, the price can range from 200 to 1,000 euros.

Driving a vehicle with the particulate filter removed or deleted is completely illegal

Be careful, because there is a lot of ignorance here. It is not only about the legal aspects; there is also the false belief that all you need to do is cut, remove and weld. But removing the particulate filter is not easy. It requires not only emptying the internal ceramic element or replacing the entire filter with a section of exhaust pipe, but also reprogramming the software. The filter’s functions are first disabled electronically via the ECU, and then the physical removal is carried out, which consists of emptying the filter.

It is also common to think that if the particulate filter is removed, it will not be detected at the ITV (MOT test). It is true that the emissions test that turbodiesel vehicles undergo is carried out with an opacimeter, which analyses the exhaust gases and can accurately determine emissions, but it does not detect whether the filter has been removed. However, ITV inspectors increasingly have more tools to detect this fraud. A simple visual inspection can reveal that the filter has been tampered with, and OBD diagnostic tools can also be connected to the vehicle to detect irregularities.

Another mistake is thinking that if a workshop removes your particulate filter, you will be able to claim if you have a problem later. Normally, if you find a workshop that carries out this operation, you will have to sign a liability waiver document.

The problems of removing or deleting the particulate filter

We have already discussed the advantages of removing the particulate filter. And also, we will not tire of saying it, that doing so is illegal. But you should also know that removing a particulate filter can cause many problems. Here are some of them:

• Engine faults. Deleting a particulate filter and carrying out the corresponding software reprogramming is not simple, and there is a risk of future problems due to malfunction, which can cause further failures. Note that this applies not only to the turbo, but also to the catalytic converters and the engine itself.
• Unfavourable ITV result. Logically, if the ITV detects that the vehicle has had its filter deleted or removed, the car will have to be presented for inspection again with a correctly fitted filter in order to obtain a passing result.
• Loss of warranty. Any tampering with the particulate filter or the car’s software is a direct reason to lose the warranty, if it is still in force.