DIAGNOSTI C S
When heavy duty vehicle technicians discuss
maintenance, the conversation usually includes
oil changes, brake checks, inspecting for coolant
leaks and tire wear.
In addition, the diesel particulate filter
(DPF) is also high on the list of vehicle
components no technician should ever
neglect. Failure to maintain the DPF and
its supportive system not only will result in
anemic acceleration and poor fuel performance,
46 Fleet Maintenance | November/December 2018
but may result in damage to the filter
itself, the exhaust system or engine.
Development of the DPF
Th e development of the DPF and its installation
on all model year 2007 and newer heavy
duty diesel engine vehicles made in the U.S.,
was prompted by the U.S. Environmental
Protection Agency (EPA) Diesel Emissions
Reduction Act. Th is initiative was implemented
to reduce particulate matter released into the
atmosphere by diesel fuel combustion, which is
believed to cause asthma and other respiratory
ailments, including lung cancer.
Th e DPF is usually made of ceramic composites
and is installed as part of the exhaust
system. Its layered walls trap soot and ash,
the byproducts of fuel and oil combustion,
preventing these residual toxins from escaping
into the air.
It is not permissible to disable the DPF system.
Not only will the system no longer operate as needed
to remove particulate matter from the exhaust
of the vehicle, but fl eets may face penalties and
fi nes if they do not adhere to U.S. EPA regulations.
Understanding the DPF
Instead of ignoring or dismantling the DPF, it’s
important for fl eets to take time to understand
they system. Th is includes the best way to maintain
it. Over time and use, soot builds up in the
fi lter, constricting air fl ow and increasing pressure
before the fi lter. Sensors, located before and
aft er the fi lter, monitor the level of soot within the
fi lter by measuring air pressure. When signifi -
cant pressure is detected, the powertrain control
module (PCM) initiates a DPF regeneration.
DPF regeneration, sometimes referred to as
regen, is designed to automatically reduce the
buildup of soot in the fi lter, and therefore reduce
the pressure in the fi lter. Regeneration should
not be confused with cleaning. DPF regeneration
is actually the burning of the larger particulate
matter into smaller ash.
Separately, cleaning a DPF involves removing
the fi lter and bringing it to a shop that uses a
thermal heating or forced air process to remove
the caked soot. Such cleanings are said to restore
the fi lter to close to 90 percent of manufacturer’s
recommended back pressure. Instead of cleaning
the DPF, fl eets may also opt to replace the DPF.
Some fl eets have started to include having the
DPF cleaned every 120,000 miles as part of the
per-vehicle maintenance plan.
Critical aspects of
servicing the diesel
particulate fi lter
With the advent of more stringent emissions
regulations on heavy duty diesel engines, it is now
more critical than ever that heavy duty exhaust
systems and their components be properly serviced.
By Michael Flink
AUTEL, INSTRUCTOR, HEAVY DUTY VEHICLE
DIAGNOSTICS
Autel is a manufacturer and supplier of professional diagnostic
tools, equipment and accessories. Flink has spent
close to 30 years in the passenger and heavy duty vehicle
diagnostics and repair industries. His experience, teaching
skills and education make him a sought-after instructor in
the continually evolving vehicle diagnostics market.
» Manual regenerations must be completed
in the shop using a qualified scan tool.
The Autel MaxiSYS 906CV tablet can
autoscan all systems and also view live
data to provide details to the technician
on how the engine is functioning.
Photo courtesy of Autel
» Technicians must plug the diagnostic tool
into the vehicle’s OBD port. A static forced
regeneration can take up to an hour.
Photo from iStock
There are three
types of DPF
regeneration: passive,
active and forced.