Understanding How a DPF System Works

Understanding how a diesel particulate filter works is essential when owning a diesel vehicle. More than knowing how to get your vehicles running, it’s important that you also know how to take good care of it when a problem arises.

That simply means you have to start understanding how a DPF system works. Today, we are going to talk on everything about DPF and how can you understand what signals your DPF is giving you.

What is a Diesel Particulate Filter (DPF)?

The term DPF stands for Diesel Particulate Filter. It is used in the diesel engine that is Euro-6 emission compliant. The manufacturers use the Diesel Particulate Filter to filter, store, and burn the soot particles which are emitted as a result of the combustion process of the diesel.

A diesel particulate filter (DPF) can remove virtually all the soot particulates (PM) from the exhaust gas emitted from a diesel engine to ensure compliance with very strict emission standards. Regardless of the actual emission limit, diesel particulate filters satisfy the needs of operators who place importance on achieving extremely low soot emissions.

Diesel Particulate Filters Mean Less Soot

The emission regulations for diesel engines are becoming stricter worldwide, which makes adjustments and developments to the drive systems necessary.

As a basic principle, DCARB’s approach to achieving compliance is to reduce emission levels by means of internal engine enhancements. Depending on the particular emission limits, it may be possible to do without a diesel particulate filter altogether. However, there is a relationship between the production of soot particulates and nitrogen oxides when internal engine measures are used if fewer soot particulates are produced during the combustion process, the quantity of nitrogen oxides increases, and vice versa.

In situations where emission requirements are strict with following standards, therefore, adding a diesel particulate filter is necessary, since it removes 90 percent or more of the soot particulates from the exhaust.This just simply means less soot and a safer vehicle for you and the environment.

The Diesel Particulate Filter System: What Happens Down There?

The Diesel Particulate Filter (DPF) is a ceramic filter that has thousands of tiny channels or honeycomb-shaped openings that trap the soot onto the channel walls and prevent the particulate matter from exiting out the tailpipe. The honeycombed inner structure is covered with a layer of a chemical catalyst that contains small amounts of precious metals, usually platinum or palladium.

Diesel cars and trucks manufactured after 2009 must have a DPF, and in some cases, a Selective Catalysts Reduction (SCR) system. These components work together to reduce, and when working properly, remove all of the harmful NOx and soot from the exhaust. Not only does this help the environment, but it also creates a much cleaner engine.

Engine oil doesn’t get as dirty as fast as it would have without all of these systems in working order. Less soot mixed with the engine oil means less of that gritty carbon forming in the oil galleys and other moving parts. This increases the life of the engine at the same time it cleans the air.

The drawback to all of this is that the DPF needs to be cleaned regularly. The soot particles attach themselves to the lining of the DPF while the engine is running. At the same time, the filter is slowly clogging with the very particulates that it’s designed to remove from the exhaust.

This process of cleaning the DPF is done through a process called regeneration. There are several different methods used by various manufacturers to clean the DPF.

Passive Regeneration

Passive self-regeneration is completely transparent to the operator and does not affect the machine’s operation or performance.

The only indication when a passive regeneration cycle has been activated is either an exhaust temperature warning light indicating the exhaust temperature is higher than normal or a message stating a regeneration cycle is in process, or both.

Active Regeneration

Active self-regeneration occurs when there is not sufficient heat in the exhaust to convert the PM being collected in the DPF. The active regeneration is self-activated by the PCM based on various inputs.

The PCM sends a command to raise the exhaust temperatures by adding a small amount of injected raw fuel upstream of the DPF. The chemical reaction of the precious metals in the DPF and the raised exhaust gas temperatures oxidizes the PM from the filter.

Filter Failures

Some diesel exhaust filter failures are a result of not allowing the regeneration to take place. This will inadvertently clog the DPF to the point that replacement is the only option. Although it can be cleaned to some degree, a portion of functionality is still lost due to the severity of the restriction.

Another problem is when it is in regeneration and the excess heat combined with the clog causes the metal casing of the DPF to expand and rupture. Which, of course, means the only solution is to replace the DPF. The DPF requires professional cleaning every 150,000–250,000 miles or 5000 hours.

Components of Diesel Particulate Filter System

The temperature sensor upstream of DPF detects the temperature of the exhaust before it enters the DPF. The integral NTC resistor changes its electrical resistance according to the exhaust temperature and then sends a corresponding voltage signal to the CDI control unit.

The CDI control unit uses the voltage signal to monitor the rise in exhaust temperature before and during the regeneration phase.

The DPF differential pressure sensor detects the difference between the exhaust upstream and downstream of the DPF. The exhaust pressure sampling pipes upstream and downstream of DPF detect the exhaust pressure difference.

Furthermore, the pressure difference between the exhaust pressures upstream and downstream of the DPF acts on the integral piezo-electric pressure sensor element. This produces a voltage in which the integrated silicon chip amplifies and passes on to the CDI control unit as a voltage signal.


Regeneration can only happen when the conditions are within the preset specifications for that motor and manufacturer’s needs. In general, most regeneration cycles are handled without the driver knowing they are taking place.

The regeneration process occurs by raising the temperature of the DPF to around 1,100°F (600°C) and enough oxygen is provided directly to the DPF. Some systems will inject extra fuel into the cylinder on the exhaust stroke which effectively sends hot gasses into the oxidation catalyst of the DPF, raising its temperature sufficiently to cause the carbon to react with the excess oxygen that was also provided. Other systems rely on a heating element just in front of the DPF to raise the temperature.

The regeneration process will continue until the pressure differential across the DPF (input and output) drops to an acceptable level. Should the driving circumstances change, for instance, the car comes to a halt and the regeneration is abandoned until the conditions once again become suitable.

Regeneration can be a noisy affair, as the engine revs up to 4,000 RPM for four minutes or more, then goes to 2,000 RPM for an additional four minutes or more. When the regeneration has completed, the vehicle will return to its normal idle, and the service light will go back off.

Selective Catalytic Reduction (SCR)

SCR is an alternative to the EGR and addresses the same issue of reducing the NOx contaminants. This system uses a solution of 32.5% urea and 62.5% denatured water called Diesel Exhaust Fluid (DEF).

This blue fluid is contained in a separate holding tank that is injected into the exhaust. When the urea mixture meets the hot exhaust gasses, it decomposes to ammonia (NH3) and CO2.

The ammonia then reacts with oxides of nitrogen in a second catalytic converter to form a harmless output of nitrogen and water. The advantage is not only a reduction in NOx, but a reduction in the use of the EGR. This means more efficient combustion, reduced PM output, and improved fuel consumption.

Trust The Experts for Your DPF

At DCARB, we have a unique and more client-tailored approach service. We have experts when it comes to providing you with a better and high-quality DPF (DPFParts). we have the best technicians to provide you the utmost cleaning, installing, repairing, and maintenance service (DPF Cleaning).

If you wanted to learn more about DPF, talk with our experts today!