april2022 - 29

It should be noted that the exhaust side of the
DPF provides the most detail for determining the
condition of the core. Good lighting will aid in the
inspection process, Velocity advised. The dealer
also detailed a number of specific areas to inspect
when assessing a DPF for damage. According to
Velocity, these include:
Surface damage: Gouges or scrapes
Scrapes and gouges on the surface of the core
cannot exceed 1/2 " in length and 1/4 " in width
and can be no deeper than 1/8 " .
Surface damage:
Loss of substrate plugs
The loss of substrate plugs across the surface is
considered surface damage. Open cells along the
outer edges cannot exceed three rows in from the
edge. Surfaces with numerous gouges that do not
exceed the tolerance criteria cannot exceed a total
of five blemishes across the entire surface area.
Vertical cracks
Vertical cracks are visible at the surface and may
be seen on one or both sides. Vertical cracks may
propagate in different patterns that may spider
across the surface or around uniformly, parallel,
or perpendicular with the cell walls.
Horizontal cracks
To identify filters that have experienced horizontal
cracks internally, turn the filter to the exhaust or
outlet side for inspection. The exhaust side of the
filter can be identified by an embossed arrow on
the can showing flow that points to the exhaust
side of the filter or by careful consideration of the
mounting flange characteristics. The exhaust side
of the filter should have no signs or evidence of
soot. Horizontal cracks run laterally through the
brick. Cracking begins around the outer area of the
substrate brick and propagates to the center but
cannot be seen at the surface of the brick.
Internal horizontal cracks
Internal horizontal cracks in early stages leave
traces of soot in a ring around the outer edge of
the outlet side of the filter. More severe internal
cracks that have propagated across the entire brick
allow soot to accumulate in the outlet across the
entire surface in a uniform pattern.
Foreign matter
Foreign matter blocking the surface pores of
the substrate cause damage through the cells
and during removal. Contamination could be
any substance that adheres to the surface of the
substrate and restricts flow.
Fusion or melding
Internal fusion breakdown allows soot accumulation
on the exhaust side of the filter and can
be identified as spots of soot or evidence of soot
in non-conforming patches on the outlet surface.
Fusion or melding of the substrate brick and the
severity of the failure can be localized internal
hot spots known as fusion or as extensive as a
complete exothermal breakdown that can be seen
by massive deterioration of the cell walls extending
to the surface of the brick.
» Staining on an uncatalyzed filter like this
is not harmful if the cause was corrected.
Photos: Diesel Emissions Service
Brick slippage
Slipping of the brick can be identified by a reduction
of clearance from the outlet surface area to
the outlet flange of the filter can.
Can damage
Dents that exceed 1/2 " into the can constitute can
damage. Witness marks from clamps are acceptable
unless the damage is so severe as to allow
rust to penetrate through the can.
Flange damage
Flange damage is a distortion of the mating
surface of the filter can at either the inlet or outlet
clamping area. Bracket damage is a distortion of
the bracket.
Key points such as direction of exhaust flow,
specific characteristics, and substrate brick
damage and soot patterns are important when
inspecting the particulate filter core for potential
damage.
Similarly, Diesel Forward Inc., a distributor of
new and remanufactured diesel engine components
through its Alliant Power brand, details
visual DPF core inspection criteria.
The Diesel Forward process includes steps for
visually inspecting the DPF core housing and
substrate inlet and outlet faces for the following
damage:
* Cracked filter substrate
* Gouged filter substrate
* Melted filter substrate
* Soot accumulation on the DPF outlet face
DPF diagnostic considerations
Diesel Laptop's Carnes explained that DPF diagnostics
can be as simple as removing the inlet
and checking for contamination or damage-or
as complicated as running multiple on-board
diagnostic tests with a scan tool to monitor the
rise and fall of DPF pressures and the differential.
Additionally, soot accumulation on the back or
outlet side of the DPF is a telltale sign that the
filter is internally cracked.
" When a DPF is replaced or cleaned, a technician
must go into the diagnostic software and
program a reset or replacement command so the
control module knows that the DPF is now clean, "
Carnes said. " One problem that arises is when
technicians perform the resets when they are
not needed, which can throw off the calculations
inside the control module. That leads to technicians
having to perform more diagnostics than
necessary when ash has accumulated in the DPF,
but the control module may not be aware of it. "
Diagnostic scan tools offer a solution to that
challenge. Scan tools are needed for performing
a DPF service for a number of reasons, noted
Victor Rivilla, marketing director at CanDo
International, maker of a wide range of diagnostic
scan tools for commercial vehicles. For example,
they give forced regenerations the ability to
override soot levels logged in the engine ECM,
which occurs when soot loads are too high for
a passive or active regeneration. The tools are
also needed to scan for trouble codes prior to
performing a forced regeneration.
" It is also important to use a scan tool to view
live data on soot levels, soot concentration, and
DPF load before, during, and after the forced
regeneration, " Rivilla said. " Finally, after performing
the forced regeneration, the scan tool is used
to reset or turn off the DPF light. "
Steve Hoke, president of Diesel Emissions
Service, said that a sound approach to evaluating
DPFs is to use several tools to get the whole picture
on aftertreatment problems. At the same time, he
was quick to point out that DPFs are serviceable
units and should be cleaned every 75,000 to
100,000 miles.
" This keeps the volumetric efficiency of the DPF
where the manufacturer intended it to be, " Hoke
explained. " Barring no engine upset conditions
and yearly cleanings, the DPF should last for many
years. In fact, we have customers that have had
the same DPF for more than ten years. "
When it comes to sourcing replacement DPFs,
Hoke noted that current supply chain issues have
led to some lack of OEM ATS components, but
there has been steady availability of aftermarket
parts. " Fleets could assume that a branded
part meets or exceeds all OEM parameters, " he
explained. " Brand reputation should help with
this decision, and warranty length and what's
actually covered should also be included when
making a choice.
" In all cases, fleets should look to their local
truck parts supplier or specialist in the DPF cleaning
business, " Hoke added. " Most truck parts
distributors have chosen reputable companies
to partner with for aftertreatment parts. "
The importance of proper DPF inspections
» Exothermal damage caused by over
fueling or a high temperature condition.
cannot be understated. Beyond cleaning and
maintaining the filters, however, it is important
to recognize that a DPF will eventually need to be
replaced. In those cases, there are several OEMs
and aftermarket providers that offer new and
remanufactured replacements.
April 2022 | FleetMaintenance.com
29
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