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 after treatment device that traps particulate matter such as soot and ash. DPF delete shops 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.

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.

DPF delete shops 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 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

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.

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 after treatment dozer starts to inject, increasing the temperature in the after treatment 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.

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.

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 agricultural technician program created in conjunction with Fend, part of the AGCO Corporation. In just 8 weeks, students learn valuable skills to get started in their agricultural mechanic careers.