EPA-420-F-10-027

 May 2010

National Clean Diesel Campaign

www.epa.gov/cleandiesel

Diesel Particulate Filter

Operation and Maintenance

Technical Bulletin

This bulletin is intended to provide general guidance. 

Diesel Particulate Filter (DPF) manufacturers and product 

suppliers should provide more detailed device-specific 

information and training to vehicle service technicians 

on proper retrofit product maintenance procedures for a 

specific product. DPFs are currently installed on all new 

on-highway engines in the United States, and DPFs may 

also be installed on most vehicles as a retrofit device. 

DPF Operation

DPFs work by physically trapping and removing 

particulate matter (PM) from the engine’s exhaust. The 

DPF can accumulate and combust PM within the filter 

element to achieve greater than 85 percent reductions in 

PM emissions. The combustion of PM in a filter occurs 

during regeneration. During normal operation a DPF will 

cause fluctuations in exhaust backpressure as PM is 

accumulated. Consequently, a DPF is used in conjunction 

with an exhaust backpressure monitoring system. 

Backpressure Monitoring 

As a DPF collects PM, the passage of exhaust gas through 

the pores of the filter element may be progressively 

blocked, causing an increase in exhaust backpressure. 

Collected PM is combusted and reduced to ash during 

filter regeneration, effectively unblocking the pores of 

the filer element and decreasing exhaust backpressure. 

Normal filter operation will include fluctuations in exhaust 

backpressure; however, over time the accumulation of ash 

will gradually continue to increase backpressure. Long 

term buildup of ash is remedied by periodic filter cleaning. 

Engine manufacturers place limits on the exhaust 

backpressures for their engines; therefore, an exhaust 

backpressure monitoring and operator notification system 

must be installed with every DPF. If exhaust backpressure 

exceeds certain thresholds, the operator is notified that 

maintenance is needed. It is important that all vehicle/

equipment operators and fleet service technicians 

are properly trained to recognize and respond to high 

backpressure alert signals. Backpressure monitoring 

systems should be periodically inspected for proper 

operation. 

Filter Regeneration 

Regeneration occurs when the filter element reaches 

the temperature required for the combustion of the 

accumulated PM, converting it primarily to ash, gaseous 

carbon dioxide (CO2) and water (H2O). 

“Passive” regeneration occurs when the exhaust gas 

temperatures are high enough to initiate combustion of 

the accumulated PM in the DPF, without added fuel, heat 

or driver action. “Active” regeneration may require driver 

action and/or other sources of fuel or heat to raise the 

DPF temperature sufficiently to combust accumulated 

PM. Active regeneration can be accomplished either 

during normal vehicle operation or during a controlled 

event while the vehicle is stationary. During operation, 

active regeneration may use extra fuel to raise the DPF 

temperature to combust accumulated PM. An active 

system that requires the vehicle to remain stationary 

dictates the time required every shift or every day that 

the vehicle must be out of service. The frequency of 

regeneration is determined by the engine’s duty cycle, PM 

emission rate, filter technology, and other factors. When 

using an active filter, it is particularly important to follow 

the manufacturer’s instructions for regeneration. 

Diesel Particulate Filter (DPF) 
DPF Maintenance

In addition to PM, the filter also traps noncombustible 

materials resulting primarily from lubrication oil and fuel 

additives (ash). Cleaning of ash from retrofit DPFs is 

typically required every 6 to 12 months. An engine emitting 

excessive PM or experiencing inadequate regeneration will 

cause a DPF to require more frequent cleaning. Diagnostics 

should be performed to identify the cause for more frequent 

cleaning intervals. It is important to avoid excessive PM 

and ash accumulation in a DPF, so proper maintenance 

and cleaning instructions should be followed closely. A 

backpressure monitoring system should always be used 

with a DPF and periodic inspection of the monitoring 

system should be performed to confirm proper operation.

In general, cleaning requires heating the filter and using 

compressed air combined with a vacuum system to blow 

the ash from the filter and capture it in a sealed container. 

Cleaning requires manually removing the DPF from the 

vehicle and placing it in a cleaning station designed for this 

purpose. Highly automated cleaning stations are becoming 

available, allowing fleet service technicians to perform 

cleaning on-site. Professional filter cleaning services are 

also available. Costs for cleaning stations or professional 

cleaning services should be considered when purchasing 

DPFs. 

If equipment down time during cleaning is a concern, fleets 

may consider buying extra filters to have in stock at the time 

of cleaning. The filter must be reinstalled in the correct flow 

direction to maintain proper operation. Removal of the DPF 

for filter cleaning and reinstallation is typically performed by 

fleet service technicians.

It is important that all vehicle/equipment operators and fleet 

service technicians are properly trained on filter cleaning 

procedures. 

Documentation should remain with the vehicle and/or in fleet 

records which lists installation and vehicle information such 

as mileage, opacity readings, date, device model number, 

DPF serial number, installer, etc. Records should also be 

maintained to document when service is performed and 

when the DPF is cleaned. If a fleet moves a DPF between 

different vehicles, records should be carefully monitored to 

identify if a particular vehicle or device appears to require 

different service intervals than another. 

Engine Maintenance 

It is important to properly maintain vehicles and monitor 

fuel and lubrication oil consumption. A bad fuel injector or 

increase in oil consumption may be masked by a DPF. The 

DPF may be damaged by a poorly maintained engine. When 

a DPF is removed for cleaning, it may be useful to check 

the opacity of the vehicle to determine if a potential engine 

problem exists. Maintaining service records is advisable to 

track potential concerns or changes in operation.