october2023 - 15

A
n aftertreatment system failure can be a
frightening prospect for a fleet's bottom line.
That's because in the long term, the costs
related to roadside service, downtime, and
repairs can haunt a perfectly normal maintenance
budget. In the short term, tracking
down and exorcising the root cause can feel
like a futile exercise in hunting ghosts. Once
you think you've found the phantom problem-poof-it
vanishes.
To truly bust the ghosts in the machines,
first and foremost, technicians need a disciplined
approach to troubleshooting, but it
also helps to know when those efforts have
reached a dead end. To help reanimate your
trucks, Fleet Maintenance has communed
with leading aftertreatment experts to dig
up common diagnosing missteps.
Mistaken identity
One of the biggest missteps a technician can
make is to hastily presume-and take action
on-upstream leaks that could be to blame.
And this isn't something that only happens
once in a blood moon; it's actually a regular
occurrence in the shop.
Steve Hoke, president of Diesel Emissions
Service (DES), sees " NOx sensors changed
out all the time " to resolve an aftertreatment
fault code. " But a day or week later, the truck
has the same issue because replacing the
sensor didn't repair the root cause. "
The devilish DTC is summoned more
often by dosing issues or a bad electrical
connector in the harness, he explained.
" This does cause additional stress on both
the customer and shop, " Hoke added.
An OEM-label NOx sensor runs more than
$300, which isn't so scary, but then you have
to factor in labor and downtime, as well as
when the shop, either in-house or external,
can service the truck. One phantom problem
can end up costing a fleet thousands.
" There are just so many components
that have to work perfectly, " Hoke said.
" Furthermore, even the best aftertreatment
system relies on an engine that is running
almost perfectly. There's a lot to think about. "
Aside from the maligned NOx sensor,
diesel particulate filters can also be cast
in a bad light.
" The DPF always gets the blame, but rarely
is to blame, " said Jeremy Anderson, VP
of sales at FSX Equipment, a manufacturer
of DPF, DOC, and SCR cleaning equipment.
The hunt for upstream
apparitions
What are some upstream apparitions a technician
should be on the lookout for?
Don Kirkpatrick, director of reliability
and uptime at Penske Truck Leasing, offered
some guidance.
" At intake, there can be restricted air
filters and intake side leaks that can reduce
the oxygen available for the in-cylinder
burn process, " Kirkpatrick said. " Within the
engine itself, there are sensors and system
controls. Those include wiring issues, faulty
sensors and ECM, as well as failed intake
components, boost control, or fuel system. "
He added this could also include failed
internals, such as excessive oil consumption,
an
incorrect valve
adjustment,
compression loss, internal coolant loss, and
burning coolant.
" In the seventh injector, there are sensors
and system controls, clogged injector
posts, and leaking or inefficient injection, "
Kirkpatrick said.
You can't forget about the EGR either.
" There can be clogged coolers and tubes,
and carbon-packed sensors, " he reminded.
According to Hoke, the EGR has gained a
ghastly reputation for developing hotspots
and cracking. Some of that can be traced
to design issues, but other causes include
internal leaks and over-fueling.
Ryan Fox, owner of Fox Truck & Tractor
in Canton, Ohio, said the EGR cooler is the
first place he looks when a customer comes
in with a DPF-related problem.
" I have come to look at EGR coolers as
a maintenance item, " Fox said. " I would
rather just replace one at 500,000 miles
as opposed to just letting it go completely
out. That coolant can ruin a diesel oxidation
catalyst (DOC), which can create even
bigger problems. "
Fox provides in-depth maintenace tips
on his YouTube channel, Trucking & Fixing
With Ryan, and other social channels.
As a general rule, technicians should
always remember that the job of the aftertreatment
system is to clean up what's
coming out of the engine.
" When something isn't working properly
on that engine, the aftertreatment system
just can't keep up, " said Scott Meek, diesel
training manager at Diesel Laptops, a provider
of diagnostic tools, repair and parts information,
and technician training and support.
" You end up with an aftertreatment assembly
that becomes restricted. The technician
troubleshoots the aftertreatment system and
resolves that but never addresses the engine.
They send the truck on its way, but the same
issue comes up again. When it comes to solving
the toughest aftertreatment issues, solving
the upstream issue is the ticket. "
Night of the living dead DOC
The technician still has to resolve the aftertreatment
failure, too. Any upstream failures
can wreak havoc on the aftertreatment
system, starting with the DOC and creating
a domino effect.
Regarding the DOC itself, it's difficult to
know if it has failed unless there is face
plugging or other visible damage. Cleaning
a DOC won't help if the catalytic coating
has been compromised, which is nearly
impossible to detect without sending the
DOC to a lab for analysis.
" The best thing to do is think about the
relationship between components and how
the aftertreatment system works, " said Dave
Jerman, sales director for Roadwarrior Inc.,
a provider of aftermarket DPFs and other
aftertreatment parts.
If a vehicle is having regen issues, Jerman
advises that technicians use the truck's
history as a guide.
" The vehicle's ECM records every active
regen event, " Jerman said. " Download that
history and look for trends. As an average,
maybe the vehicle was regenning every 200
hours or so. Then the frequency started to
increase. The technician cleaned the DOC,
but the frequency didn't change. Then
it's important to look at vehicle service
history to see if any upstream issues may
have poisoned the DOC. If the vehicle had
a blown turbo, EGR coolant leak, or bad
in-cylinder injector within the 12 months
preceding the DPF failure, you know the
DOC has been compromised to some
degree. It's possible that the DOC isn't dead
on arrival, but it could be getting weak in
the knees. "
For
this very reason, Hoke said it's
important for a technician to perform a
DOC efficiency test. A poisoned DOC may
continue to limp along for a while. But the
DPF will continue to prematurely overload
with soot because the DOC isn't doing its job
" The DPF always
gets the blame, but
rarely is to blame. "
Jeremy Anderson,
VP of sales, FSX Equipment
» Visible soot on the outlet side of a DPF
is an indication of internal cracking. When
this is the case, the DPF should
be replaced.
Roadwarrior
october2023

Table of Contents for the Digital Edition of october2023
