
Diesel engines pack a punch, providing the powerful performance you need to haul loads reliably and efficiently. One drawback of diesel engines is that they produce emissions with harmful pollutants that can damage the environment and affect human health.
To help minimize pollutants and meet international emission standards, modern diesel trucks use emission control systems and devices, such as diesel particulate filters. Learn more about these filters and how they help your truck maximize fuel efficiency while producing fewer emissions.
What Is a DPF?
A diesel particulate filter (DPF) is an exhaust after-treatment device. It is located in a diesel engine’s exhaust system between the engine and the tailpipe. The device is made of ceramic, offering thermal resistance and stability. It uses a filter with a honeycomb structure and microscopic pores that trap pollutants, ash, and carbon, or soot, particles from the exhaust gas.
DPFs work alongside other systems to help reduce harmful emissions. The exhaust gas recirculation (EGR) system lowers nitrogen oxide (NOx) emissions by recirculating exhaust fumes and lowering combustion temperatures, while DPFs catch and store pollutants from exhaust gas before they enter the environment. A diesel oxidation catalyst (DOC) helps minimize the amount of soot that enters the DPF.
This efficient and effective technology increases fuel economy and prevents the black smoke that’s common with diesel engines. How long a DPF lasts will depend on how often it is cleaned and maintained.
How DPFs Work
DPFs collect exhaust gas from the engine and push it through honeycomb-shaped channels with blocked ends. The exhaust gas goes through the filter, while the soot particles and pollutants remain behind.
A DPF quickly accumulates soot. However, the filter has a limited capacity to hold it. The trapped pollutants need to be removed regularly to ensure proper filter performance. When the filter fills with pollutants, regeneration initiates.
DPF Regeneration
Regeneration burns off excess soot within the filter, turning it into carbon dioxide that can pass through the filter. This process is necessary to restore soot collection capacity. Regeneration needs to happen periodically, but how often it occurs depends on filter technology, pollutant emission rate and the engine duty cycle.

The regeneration process can only occur once the filter reaches the right temperature to combust the pollutants, usually about 600 degrees Celsius or 1112 degrees Fahrenheit. Regeneration can happen in two main ways:
- Passively: The filter regenerates naturally during the engine’s regular operation. Operators don’t need to initiate the process, and it does not affect engine performance. Temperatures usually reach high enough to activate passive regeneration during long drives at a steady speed along the highway.
- Actively: Active regeneration occurs when the filter temperature is too low to stimulate passive regeneration on its own. This controlled cleaning process is activated by the vehicle’s engine control unit when the filter reaches a specific soot capacity. The engine releases more fuel into the exhaust stream to raise temperatures and initiate the cleaning process.
Both passive and active regeneration occur automatically without driver input. Trucks often feature dashboards with lights that signal when regeneration happens.
Symptoms of a Blocked DPF
Your truck’s DPF may be blocked if you notice signs such as:
- A dashboard warning light: Most modern diesel engines have sensors that monitor engine performance. These sensors can notify you when the DPF is blocked and when regeneration processes are failing to clear the blockage.
- Increased black smoke: The DPF is supposed to trap soot that escapes as visible black smoke and instead leave behind a cleaner exhaust gas. If you see more black smoke coming out of the exhaust pipe, you may have a blocked DPF.
- Frequent regenerations: A DPF with a clog will require more regenerations to clear the blockage. You may notice more frequent regenerations when the DPF is filled with soot.
- Decreased engine performance: Blocked DPFs can cause exhaust gas to build up and affect engine performance. The engine may lose power, refuse to start or make loud popping noises.
- Greater fuel consumption: A DPF can help maintain a consistent exhaust flow, but when it becomes clogged, the flow is restricted instead. Clogs can reduce fuel efficiency, making the engine work harder and consume more fuel to operate normally.
Causes of a Blocked DPF
The DPF’s purpose is to trap and hold onto pollutants. DPF regeneration is designed to remove these pollutants and help the DPF continue to collect soot and ash, but regeneration can only happen when the filter reaches a specific temperature.
If you drive short and low-speed journeys, or if you drive on low fuel levels, the engine may not get hot enough to activate regeneration. Without regeneration, the DPF fills with pollutants and becomes clogged.
A few other causes behind a blocked DPF include:
- Incorrect oil: Traditional engine oils use metallic additives that can increase ash accumulation and lead to clogs. To reduce clogs, you should use engine oils with a lower tendency for ash generation.
- Faulty DPF sensors: The sensors that monitor DPF status may malfunction. Sensor errors can disrupt the regeneration process, leading to more soot accumulation.
- Low-quality fuel: Contaminated fuel can have higher particulate levels. The more particulates passing through the filter, the easier it is for the DPF to clog.
- Mechanical problems: Engine problems, such as a faulty fuel injector or broken EGR valve, can increase the soot released into the exhaust system. More soot means more clogs in the DPF.
It is critical to address clogs as soon as possible. Blocked DPFs can lead to engine problems, higher emission levels and decreased fuel efficiency. If soot and ash are left in the filter for too long, they can harden and become difficult to remove.
While it is important to make sure regeneration is happening, you will also need to have the DPF cleaned regularly. Regeneration processes can only remove so much of the soot and ash, so cleaning is essential to completely remove everything left behind.

Learn More About DPF Cleaning and Replacement From Inland
Your DPF plays an important role in lowering your truck’s emissions and keeping your engine running efficiently. Take care of your truck’s engine and DPF by working with the professional technicians at Inland. Our team knows how to clean DPFs safely and thoroughly. When needed, we can replace your DPF to ensure optimal engine performance.
For over 70 years, Inland has been committed to providing the comprehensive sales, service, and parts solutions our clients need.
Are you ready to get started? Find your nearest full-service location to schedule DPF cleaning or replacement service and connect with us online, over the phone, or in person.