DPF (Diesel Particulate Filter): All You Need to Know

All modern gasoline cars (introduced in 2009) come equipped with a DPF – Diesel particulate filter. The function of the DPF is to filter and remove out toxic particles out of the exhaust.

Automotive experts say that a good DPF particulate filter is one which filters 80% of the particles.

A lot can go wrong if there’s a problem with the DPF. Some common problems include the filters getting clogged with soot, which prevents them from functioning properly.

The role of a DPF is to filter soot, which can cause environmental damage and breathing problems. This is why it is important to make sure it’s filtered out and the environment is safe and clean.

What Is a Diesel particulate filter? DPF system?

Diesel particulate filter
DPF filter. Credit: Wikimedia.com

To put it in the most simplest term, DPF is a filter that traps the soot and filters it.

However, a car is meant to generate a lot of soot and the DPF system might not be able to hold it all. Therefore, the DPF needs to regenerate (empty itself) to prevent blockage.


The black smoke that we often see in diesel vehicles is the unfiltered soot coming out of the exhaust. When you have a DPF, you can filter out this soot. The job of the filter is to minimize the harmful particles that are released from the exhaust.

There are two kinds of regeneration processes that take place during the process, active and passive.

Passive Regeneration:

This occurs when you are driving your vehicle. To trigger this process, you must drive the vehicle for at least 15 minutes and at 40 mph. When you do so, the exhaust heats up and starts burning the soot off.

Active Regeneration:

However, if you do not succeed in triggering passive regeneration then active regeneration takes place. During this, the temperature of the exhaust gases is increased and more fuel is injected and diesel particulates are oxidized.

What If My Diesel Particulate Filter Is Blocked?

what is Diesel particulate filter
DPF in car.
Credit: Flickr.com

If your diesel particulate filter is blocked then it means that the DPF hasn’t been burning the soot and it is clogging the filters.

This happens when the vehicle does not get hot enough to burn the soot. This usually occurs due to the vehicle not being driven for a long time. This is not a good thing ass the soot can continue to accumulate and block the filters.

When this happens, your car will display a DPF engine light error and you must take it to a mechanic or buy an obd2 scanner to read the code and come up with a possible solution.

The cause of a DPF engine light is mostly a clogged filter. You can correct the error by unclogging the filter. In some cases, the filter might need to be replaced.

Unclogging the filter involves regenerating the filters manually and removing the accumulated soot from it.

If you are not confident at doing it on your own then going to the mechanic is your best bet.

Why Does My Diesel Particulate Filter Gets Blocked?

Wall-flow diesel particulate filters  
FAP-Filter Peugeot.
Credit: commons.wikimedia.org

There can be many reasons for the DPF to get blocked, such as:

Faulty EGR:

EGR valves are designed to recirculate the harmful emission back into the DPF to get it filtered further. This minimizes the soot and the emissions.

However, sometimes, these valves can malfunction and fail to recirculate the particulates. As a result of which, more and more amount of soot is accumulated in the filters causing it to get blocked.

Feeding Wrong Oil To The Engine:

It’s important to use the oil that is compatible with your car’s engine. Feeding cheaper oil into the engine can sometimes affect the performance and cause soot accumulation.

Faulty Fuel Injectors:

When the fuel injectors malfunction, they provide too much diesel fuel into the fuel mixture. The result is an excessive generation of soot that can eventually clog the filters and block the DPF.

Malfunctioned Turbo Charger:

When the turbocharger fails to work, it might leak a lot of oil into the fuel system. Thus, drowning the DPF in engine oil and clogging the filters.

Not Driving Much:

If you are driving your car for less than 15 minutes and turning the engine off, then you are affecting the DPF as well. Short journeys clog the DPF and lead to DPF check light errors. This, however, may not happen in newer models.

How Should I Maintain A Diesel Particulate Filter?

How Should I Maintain A Diesel Particulate Filter?
DPF retrofit installation. Credit: commons.wikimedia.org

You can keep the DPF of your car in good condition by following these easy steps:

Make sure that you ride at least 15 minutes at 40 mph. This will help the DPF regenerate soot on its own, clean the filters, and continue the cycle. Failing to do so won’t active passive regeneration and may cause you further problems.

Avoid using biofuel diesel because they contribute to burning an excessive amount of soot which the DPF might not be able to handle.

Always use the specified and compatible engine oil. Failing to do so can affect the performance of the DPF and clog the filters. Use ash oil instead because it helps in the regeneration process.

Bonus: Best OBD2 Scanners Review and Comparison 2021

What To Do If Neither Active Nor Passive Regeneration Work?

In such a scenario, your car will display a warning light to get it checked.

Continuing to drive under the warning light can make the problem severe and cause the DPF to get severely blocked. This is the time when the engine might go into limp mode and won’t respond until the blocked soot is removed.

Failure of active and passive regeneration leaves you with one option only, force regeneration. Here’s where you will have to take your vehicle to a mechanic. It’s a costly process.

The Bottom line

If you have a diesel operable car then make sure to have the EGR valves, turbochargers, fuel injectors checked. Other than that, drive faster and avoid short journeys.

This way, you can make sure that your DPF works without any problem. You can also use OBDII scanners that come with advanced functionalities to help identify and fix the problem.

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