Everything You Need to Know About Diesel Particulate Filters


Whether you own a diesel-powered vehicle or aspire to become a diesel technician, it’s important to understand diesel particulate filters and how they work.

Diesel particulate filters play a critical role in the functioning of diesel-fuel cars and trucks. Failing to maintain these filters can lead to significant (and costly) consequences for the vehicle.

Follow along as we share what diesel particulate filters are, signs of a blocked filter, types of regeneration and more.

What Is a Diesel Particulate Filter?

If you’ve been exposed to the world of diesel, you have probably wondered, “What is DPF?”

A diesel particulate filter, or DPF, is an exhaust aftertreatment device that traps particulate matter such as soot and ash. A DPF typically uses a substrate made of a ceramic material that is formed into a honeycomb structure. 

In order to reduce emissions from diesel vehicles, diesel particulate filters capture and store exhaust soot, which must be periodically burned off to regenerate the filter. The regeneration process burns off excess soot deposited in the filter, which prevents harmful exhaust emission and the black smoke you commonly see emitted from diesel vehicles when accelerating.

Engine manufacturers use DPFs to trap particulate matter in order to meet the EPA 2007 emission standards. 

What Are the Symptoms of a Blocked Diesel Particulate Filter?

Oftentimes, blocked diesel particulate filters are caused by short journeys at low speeds. Vehicles operating at low speeds on short journeys are unable to meet the requirements for the filter to clean itself.

DPFs can also fail due to poor servicing. The lifespan of a diesel particulate filter varies based on the application. For example, the Cummins ISX15 engine’s filter has an interval for cleaning up to 400,000 to 600,000 miles—although it will need to regenerate before hitting the 400,000 mile mark.

DPFs may fail sooner if they are not well maintained. Additionally, filter blockage can be caused by the use of the wrong type of oil, performance modifications, using low-quality fuel or even running the car frequently on a low fuel level.

So how can you tell if your filter is blocked? Typically, when the filter becomes clogged or an error occurs in the system, an orange light will appear on your dashboard. This light varies based on manufacturer, but commonly appears similar to the image below. When this lights up, you know your filter is most likely blocked, and a regeneration may be required.

Just like there are two main particulates being filtered, there are two types of cleanings that are required. Regeneration cleans out the soot by converting the carbon to carbon dioxide, and the ash is removed by removing the filter and cleaning it in a machine with compressed air.


Graphic for diesel particulate filters


Diesel Particulate Filter Regeneration: How Do I Maintain a DPF?

The key to maintaining a DPF filter is to ensure it’s able to regenerate itself when it fills with soot (triggering the warning light). The two types of generation include passive and active.

Passive Regeneration

Inside the aftertreatment device (ATD), the exhaust first passes over the diesel oxidation catalyst (DOC), then passes through the particulate filter, which traps soot particles. Passive regeneration happens when heat in the engine builds to the point where soot, or carbon, is combined with oxygen to create carbon dioxide. Since carbon dioxide is a gas, it can pass through the filter.

Ash, on the other hand, is already a byproduct of combustion, so no amount of heat from the engine can convert it. Over time, the ash will build up to the point where the filter has to be physically removed and cleaned. This filter can then be reinstalled and reused.

Passive regeneration occurs as the vehicle is driven normally under load; the driver is not aware that it is happening. It may not always keep the DPF clean over the course of the workday, so the filter may have to undergo active regeneration. 

Active Regeneration

Passive regeneration is part of normal engine operation, however active regeneration requires the engine to take action. For example, a truck fully loaded with 80,000 pounds moving down the highway will create enough heat in the engine for a chemical reaction to occur—which is passive regeneration.

Active regeneration takes place when the engine isn’t creating the heat it needs. For example, this may occur in a truck that’s not fully loaded. Once the soot level reaches a certain point, the engine injects fuel into the exhaust stream, which goes over the oxidation catalyst and oxidizes the fuel to create heat. The heat created from the fuel oxidizing is then used to convert soot to carbon dioxide.

Both active and passive regeneration happen automatically and without driver input. Active regeneration can occur automatically any time the vehicle is moving. The exhaust gas temperature could reach 1500℉ (800℃). 

Active regeneration is unknown to the driver with the exception of some additional dashboard lamps. The biggest sign to look for to determine if it is taking place is the high exhaust temp light, which will turn on once the aftertreatment doser starts to inject, increasing the temperature in the aftertreatment device.

When Passive and Active Regeneration Don’t Work

When operating conditions do not allow for DPF cleaning by active or passive regeneration, the vehicle may require an operator activated parked regeneration. 

In order for this to take place, the vehicle must be standing still. The driver or technician brings the engine to operating temperature and initiates the parked regeneration by activating the dash controls. This may take anywhere from 20 minutes to an hour, depending on ambient conditions and type of engine or DPF system.

Before initiating a parked regeneration, it’s critical for the driver or technician to ensure the exhaust outlets are directed away from structures, vegetation, trees, flammable materials and anything else that may be damaged or injured by exposure to high heat. Not all DPF systems have a parked regeneration feature.

How Much Does it Cost to Replace a Diesel Particulate Filter?

Replacing a diesel particulate filter can be pricey. A new filter from a car manufacturer can cost anywhere from $3,000 to $10,000.

It’s no secret that as cars and trucks age, their value decreases. Oftentimes, the price associated with replacing a DPF in an older, higher mileage car or truck is more than the value of the vehicle itself. It’s much easier (and more affordable!) to clean a diesel particulate filter than it is to replace it, which is why understanding how these filters work and performing regular maintenance is so important.

If a parts supplier charges less for a DPF, be wary—the filter must be the correct type for your vehicle. Otherwise, you will most likely end up spending more on repairs.

Train to Become a Diesel Technician 

If you’re fascinated by the complexity of diesel-powered systems and love the roar of a diesel engine, consider turning your passion into a career by training to become a diesel technician.1 At Universal Technical Institute, you can prepare for an exciting career in the field in less than a year.7

Once you complete your core training program, you can decide to further your education with one of our specialized diesel programs. One of these is the 12-week Cummins Engines program, where students have access to the manufacturers' full line of diesel equipment for hands-on training.9 Depending on the campus, students can earn Cummins' qualifications that prepare them to complete warranty work at an authorized Cummins dealer or distributor!

To learn more, request information today. We’ll get you in touch with an Admissions Representative who can answer your questions and help get you started on your journey!

UTI Campuses That Offer Diesel Mechanic Training

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1 ) UTI is an educational institution and cannot guarantee employment or salary.
2 ) For program outcome information and other disclosures, visit www.uti.edu/disclosures.
7 ) Some programs may require longer than one year to complete.
9 ) Does not include time required to complete a qualifying prerequisite program such as UTI’s 45-week Diesel Technology program.

Universal Technical Institute of Illinois, Inc. is approved by the Division of Private Business and Vocational Schools of the Illinois Board of Higher Education.


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