Portland | (360) 518-1482

Clackamas | (503) 656-4151



Diesel trucks have formed the backbone of America’s highway transportation fleet for many decades, but they have also been historically associated with air pollution problems. However, an exciting technology known as diesel particulate filtering (DPF) has come close to eliminating diesel engine soot production.

In fact, today’s trucks emit only about one percent of the soot produced by a truck manufactured in the mid-1980s, and much of this is due to the use of diesel particulate filters. There is no doubt these remarkable devices have contributed environmental and health benefits to the nation and beyond.

It is important to understand how diesel particulate filters achieve such amazing results, as performance is dependent upon proper operation and maintenance. Technicians aren’t the only ones responsible for understanding diesel particulate filters, as drivers also have a duty to provide ongoing maintenance. A failure to keep filters maintained can lead to engine problems and expensive repairs.

Below is more information about the operation of diesel particulate filters as well as guidance for maintenance and upkeep of these important devices.


Soot consists of carbon molecules and is a byproduct of any combustion process, including diesel engine operation. Traditionally, soot production was considered a normal consequence of diesel engine use. However, research has shown that soot contributes to significant health problems, including cancer, and it also does environmental harm.

As a result, state, federal, and international standards now require that soot emission levels be kept low. In response, manufacturers fit new trucks and retrofit existing vehicles with diesel particulate filters to capture and dispose of soot.


Diesel particulate filters are fairly simple in design, though many depend upon computer technology for functioning. Essentially, diesel particulate filters use media to capture the fine soot particles, then perform a purge that converts soot to gases.

The filter media can vary depending on the specific application, but they commonly use ceramic or ceramic composite materials in large trucks. Metal is also used for some filters, and some filters use paper in onetime, non-reusable units.

The key factor that makes reusable diesel particulate filters work is the regeneration cycle. Once a filter accumulates a certain amount of soot, heat enters into the filter media, and it burns up the soot. The only residue left after regeneration is a small amount of ash, which is anything that can’t be consumed by the heat.


Diesel particulate filters use varying types of regeneration cycles, including manual, semi-automatic and automatic methods. Manual regeneration requires a driver to initiate the regeneration cycle manually by following a set procedure.

In the case of fully automatic regeneration, drivers don’t usually need to do much except observe. A computer controls the process by monitoring back pressure and initiating regeneration whenever back pressure reaches a certain threshold.

At that point, the computer may cause engine RPMs to elevate to increase engine heat, or it may allow heat to flow through the filter during highway travel. Regardless of the specific method, the computer initiates the action and terminates it whenever the soot is consumed.

As someone responsible for a diesel truck equipped with diesel particulate filtration, your role is to know what kind of filter is on the truck and how or when to use the regeneration cycle. In addition, diesel particulate filters require periodic cleaning to remove accumulated ash; that means you will need to take the vehicle and filter to a technician for special servicing.

Most importantly, you should be familiar with diesel particulate filter documentation and adhere to any recommended maintenance and other action items. Overlooking such tasks can result in damage to the filter.

If you have questions about your truck’s diesel particulate filter, be sure to contact S&T Truck Repair for help. Our professionals are ready to assist you in whatever way they can.