DPF Regen Cycles and How to Reduce Them


Most three-quarter ton and larger diesel trucks were mandated to have a diesel particulate filter (DPF) by the Environmental Protection Agency in 2008. As early as 2007, DPFs were standard on medium and heavy-duty trucks in the USA and Canada, and most types of diesels built from 2009 to the present have a DPF.

In the most basic terms, a DPF assists in emissions control. Its purpose is to catch any remaining particulates left from the combustion cycle of a diesel engine. Each combustion cycle within a diesel engine will generate some level of unburned components of diesel fuel; for example,  carbon and other particulates. These deposits accumulate into visible smoke from the truck’s exhaust stacks. The truck’s DPF captures many of these particulates and helps eliminate dirty exhaust emanating into the air.

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DPFs are required to capture at least 90 percent of particulate matter to meet strict environmental regulations. A properly functioning DPF prevents any legal and financial penalties for non-compliance.


This is the process of cleaning the DPF of all particulate matter and soot, and there are multiple ways that DPF regen cycles can occur. DPFs are designed using a ceramic honeycomb structure that traps and stores particulate matter from the exhaust into microscopic pores. After a while, the pores fill up making them less effective in capturing debris and soot.

Perpetual operation of a diesel truck will expose the filter to particulates that will make it clog, so the design of the DPF allows the filter to clean itself to a point by burning off the accumulated soot at high temperatures and with the use of diesel exhaust fluid (DEF), thus converting it to ash and other less harmful materials. If you’ve ever turned the heat up on a grill to clean burnt-on food off the grates, you’ll understand the basics of this regeneration process. 

After a successful DPF regen, the filter becomes more efficient at capturing microscopic particles in the truck’s exhaust gases. This makes airflow, intake, and outflow, more efficient and causes less stress on the engine. 

Over time, however, there is a buildup of ash and the DPF system will need a manual cleaning by a technician, which is costly in terms of downtime and maintenance costs. Therefore, it is important to make the most of DPF regeneration to significantly extend the amount of time before a manual intervention becomes necessary. 

“A regeneration cycle occurs by essentially ‘cooking’ the filter clean again,” says Kyle Nace, Response Equipment Specialists. “The DPF regen contains the heat of the exhaust, adding up to temperatures exceeding 1,000 degrees Fahrenheit, so that the filter is depleted of its buildup and returns to proper functioning capabilities.”


DPF regen cycles can be passive, active, parked or forced. DPF regen is initiated by the ECU.

Passive regeneration occurs naturally under steady driving when the engine achieves the required operating temperature. Under normal highway driving, passive regeneration takes place as the catalyst in the DPF heats up enough to oxidize the soot and turn it into CO2. The CO2 exits through the exhaust stack while any residues left behind are converted into harmless ash that collects in the DPF canister. The process is continual, so whenever the vehicle reaches operating temperature, under steady high engine loads, the DPF will begin passive regeneration.

Over time, passive regeneration is not enough to prevent soot from building up in the DPF and that’s when the second stage of cleaning is used, an active regeneration. The truck engine computer indicates that the DPF needs cleaning, and if the operating temperature is high enough, it automatically initiates an active regeneration. 

In general, active regeneration begins when a small amount of fuel is introduced into the exhaust stream between the turbocharger and the DPF. This fuel is atomized into an extremely fine spray that does not burn. Instead, when it contacts the catalyst on the DPF, it generates intense heat, upwards of 1,100 degrees Fahrenheit, that oxidizes any remaining soot on the ceramic filter. Unfortunately, this may take place once a day, depending on the type of driving and can last 30 minutes or more. During this time, a lack of power may be noticed by the driver.

If an automatic regen had started but was interrupted when the vehicle was stopped, and cleaning needs to be continued the vehicle information system will call for the driver to perform a manual or “parked” regeneration. Parked regens are active regenerations initiated by the driver when the vehicle is stopped and engine running. Usually there is a dash switch for initiating a parked regen.

A forced regeneration is done by a mechanic using specialized control software. This is the final step before a costly replacement of the filter is required. Filters are designed to last well over 100,000 miles and will eventually need to be replaced. Using the proper fuel and oil goes a long way in maintaining the life of the DPF system.


DPF regens are a necessity and valuable to both the truck and the environment. Here are a few reasons why regen is essential for diesel engines.

Reduction of emissions: The primary objective of the DPF is to capture particulate matter and soot from the exhaust, thus preventing harmful emissions from being released into the atmosphere. Regular regeneration of your DPF burns the accumulated waste and ensures its effective operation, thus reducing emissions and meeting environmental standards. 

Maintaining engine performance: A clogged DPF may decrease engine performance and increase fuel consumption. In some cases, it may cause the engine to enter “limp mode,” a reduced power mode that protects the engine from damage. Proper DPF regen maintains the filter’s capacity to trap soot, thereby ensuring the engine runs at optimal performance. 

Preventing expensive repairs: The costs can be significant if the DPF becomes clogged enough to necessitate manual cleaning or replacement. On average, it costs $2,000 to $10,000 to make a DPF replacement in your truck. Sufficient regeneration extends the DPF life span and helps avoid costly situations.


There is no predefined number of regens to be expected. Depending on the driving habits, load, terrain, idle time, maintenance, and upkeep of the truck, all play factors in the amount of regens that occur. Less regens may be required with proper maintenance and attention to your truck’s general upkeep. If the engine is underperforming and a continual dirty exhaust is occurring, then many regens may be required. Multiple regen cycles can happen per day if a truck is in heavy operation. With numerous regens come mounting costs and interruptions in daily use.

For this reason, many manufacturers and fleet managers recommend the use of a quality fuel additive to reduce regen cycles and preserve the quality of injectors. The right fuel additive will improve cetane levels and clean the injectors. Clean injectors produce the best spray pattern and optimize diesel combustion. Increased cetane leads to a more complete burn of the fuel for improved fuel mileage and a lower quantity of particulate matter in the exhaust. 

Less particulate going into the filter also extends the filter life, as the regenerations lessen, and it will last more miles before replacement. The addition of an additive that improves the quality of the fuel is the start to improving performance, reducing regen cycles and increasing DPF life.


To learn more about DPF Regen Cycles and how to reduce them, visit 

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