DPF (Diesel Particulate Filter): What You Need To Know

Introdution to DPF – Diesel Particulate Filter

Diesel engines have incomplete combustion in their engines. This means that not all of the particles in the diesel fuel combine with oxygen and burn up. The particles that remain are known as soot.

These particles are usually tiny. However, their effect on the environment is quite visible as they cause tremendous levels of pollution. The types and levels of emissions produced by the engine are dependent on the type of diesel engine.

The age of the engine and the emissions specifications that the engine was designed to meet are crucial factors in this equation. The solution to reducing these high levels of pollution was found in the form of DPF. This stands for Diesel Particulate Filter.

What is DPF?


The DPF is a type of filter that captures and stores the soot exhausted by a diesel engine.

Its sole purpose is to reduce the levels of emissions from diesel engines. Most DPFs can filter as much as 85% of the soot while better-designed filters can reach 100% filtration rate. The higher the efficiency levels the better for the vehicle and the environment.

Because diesel particulate filter systems normally store the soot that they filter, they tend to get full. Some types of DPFs are designed for one single use only. This means after the filter gets full, it is disposed of and replaced with a new one.

Filter regeneration

The other type of DPF system is designed to burn off the accumulated soot. It does this by the use of a catalyst or by the aid of a fuel burner. A fuel burner raises the temperature of the soot to combustion levels.

The DPF systems with the fuel burners are rather complex systems. When the DPF is full, the engine is programmed to run in a manner that elevates the temperature of exhaust gasses. The system also has an extra fuel injector that injects fuel and a catalyst into the exhaust stream.

This then burns off the soot from the DPF. There are several other ways and systems that burn the soot on the DPF. This process is known as filter regeneration.

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A video about  Diesel Particulate Filter:

Filtration capacity

Newer models of DPFs can filter up to 95% percent of all harmful soot. This reduces pollution by a large percentage.

However, the quality of fuel put in the car is a large determinant of the number of emissions. Diesel fuel that is low in Sulphur has fewer particles that can easily be filtered by the particulate filter.

Then, the pressure at which the diesel fuel is injected into the engine determines how many particles will be formed.

What causes a diesel particulate filter blockage?


The main cause of a DPF blockage is driving for short trips at low speeds for a long period of time.

Filter regeneration can only occur at speeds above 40 miles per hour or 64km/h. Therefore, if a vehicle only drives at low speeds in town traffic, it will need periodic trips at higher speeds to clean out the filter.

If you fail to drive your car regularly at higher speeds, the regeneration process will not function as it should. This means that soot remains stored in your DPF for a long period of time. When this soot remains unburnt, your DPF will block completely causing damage necessitating replacement.

Some newer vehicle models come with a much more advanced system known as parked/passive regeneration. This DPF system raises the RPM of the vehicle to above 1400RPM when parked. This increases the exhaust temperature, therefore, regenerating the DPF while parked.

How do I tell if my DPF is blocked?

The main sign of a blocked DPF is the DPF warning light on the dashboard. This tells you to take at least one trip for 15 minutes at speeds above 40mph. It should clear after this.

Other signs include a black smoke from the exhaust system. The exhaust gasses could also have a pungent odor and are quite hot. Cooling fans constantly running is another indication of a blocked DPF.

Lastly, a slight increase in the amount of fuel consumed by your vehicle is an indication that your DPF could be blocked. If you continue driving at low speeds after the DPF warning light comes on, the excessive blockage will occur. This will force you to replace the entire DPF system.

How do I maintain a DPF?

Drive faster

As mentioned above, faster driving will save you money in the long run. This is because the active regeneration process can only occur at high speeds. The RPM rate and engine temperature are also factors of the regeneration process.

DPF regeneration will not occur unless the conditions are met. This will lead to blocking and damage to your DPF system. Find out the exact conditions, speeds, and duration of fast driving that are most suitable for your vehicle’s DPF.

Choose the recommended oil for your vehicle

Selecting the recommended oil for your vehicle means that your engine will produce as few emissions as possible. Make sure that you always use the engine oil that is recommended by your vehicle’s manufacturer.

Most manufacturers recommend oils that are low in Sulphur. This means your engine produces lower Sulphated ash. This is a product of the combustion in the diesel engine that causes blockage.

Regular checking of EGR valve

The EGR valve is designed to recirculate carbon and soot. With time, it could get clogged with the same substances. This will cause it to stay open for longer than it should or even remain open the whole time.

Effectively, the amount of soot and carbon being fed back to the engine will increase. A faulty EGR valve might cost you a lot so it is proper that you have this regularly checked.

What to do if neither passive nor active regeneration work

If neither passive nor active regeneration is occurring, it is indicative of a larger problem with your DPF.

The first step you should take is to diagnose the issue. To do this, you need a vehicle diagnostics scannerMake sure the scanner works with diesel engines and can scan DPF systems.

After understanding the nature of the problem, you can decide whether it is something you can fix by yourself.

If not, it would be best if you took the vehicle to a professional mechanic. Then, they can fix the error and return your car to optimal functionality.

Bonus: 10 Best Automotive Diagnostic Scanner Review 2018