february2022 - 18

DOC (diesel oxidation catalyst), and SCR filters go
bad because of something else that's happening.
So I set those filters aside as the root cause. Now
I'm focused on the DEF (diesel exhaust fluid) and
NOx sensors. "
This truck had a dozen active codes. Freeman
found one that said DEF quality was insufficient at
the downstream NOx sensor. The doser is directly
upstream from that sensor, so Freeman knew the
DEF wasn't concentrated enough.
" I began reviewing the repair information that is
included with our diagnostic tool, " Freeman related.
" I saw that this particular code can happen
when the DEF tank is refilled. So I checked the
DEF tank and saw that it was full, but the fuel tank
was only a quarter-full, which is odd.
" The repair information also says a regen can
solve this issue, so I attempted that, " Freeman
continued.
" As I'm watching my computer
screen, I see that the doser is going back and
forth between 0 and 50 psi. That suggests a problem
with the doser line. After it ran a while, the
pressures came back up to 120 or 130 psi like
they should. "
As it turned out, the driver had allowed the
vehicle to run out of DEF, forcing the vehicle into
derate. The driver then refilled the DEF before
calling the shop. But in the meantime, air had
built up in the doser line, causing the DEF quality
code to trigger. Once this root cause was solved,
Freeman helped the technician follow the repair
procedure to properly clear the 3712 and 3714
codes, which includes three engine cycles so the
ECM can perform a self-test.
As with unnecessary forced regens, sometimes
a technician's instinct is to react to a fault code by
18 Fleet Maintenance | February 2022
Tailoring maintenance
to DPF needs
In addition to upstream problems, there are certain
applications that place extra burden on a DPF.
" An emissions system needs three things: time,
temperature, and pressure, " said Chris Hough, vice
president of maintenance design and engineering
for Penske Truck Leasing, a provider of commercial
truck leasing, fleet maintenance, truck rentals,
and used-truck sales. " If you don't give the system
enough time to build up enough heat and pressure,
it is never going to cleanse itself (passive regen).
A truck hauling a heavy load from coast to coast
will likely have very limited DPF issues because
it has the time to do what it needs to do. On the
swapping out a part. But on a vehicle with multiple
ECMs, understanding the entire layout is key.
" When you get an aftertreatment code, it could
be the DPF, the DEF, or maybe none of the above, "
said Bruno Gattamorta, vice president of sales and
marketing for Cojali USA, a provider of diagnostic
tools and other technologies. " With our Jaltest
Troubleshooting Guides, there is an option to troubleshoot
by symptoms as opposed to fault codes.
So maybe there's a problem with the injectors
dosing too much and causing a problem in the
combustion chamber. Then the EGR valve functions
out of sync and there's a snowball effect. The
code is for the aftertreatment, but the problem is
really the engine. Having the right diagnostic tool
to show a holistic view of the vehicle can be the
difference between a one-hour fix and an endless
array of parts, dealer trips, and frustration. "
» A Penske Truck Leasing ceramic oven,
dust collector, and pneumatic DPF cleaner.
Photo: Penske Truck Leasing
other hand, a city delivery vehicle may run into
a lot of issues. "
As discussed in TMC RP 355A, numerous
factors can influence DPF maintenance intervals,
including:
ÜHigh oil consumption
ÜIncreased engine wear on higher-mileage engines
ÜSulfur level of diesel fuel in excess of 15 ppm
ÜCertain supplemental oil and fuel additives
ÜEngine failures (i.e., turbocharger, wear metals,
fuel injectors, etc.)
ÜBoost and intake leaks
ÜMalfunctioning or plugged dosing injector valve
ÜDuty cycle (i.e., low-load operation or extended
idling)
Fleets have benefited from vastly improved
DPF designs. As Otto pointed out, typical
cleaning intervals used to be in the 250,000to
300,000-mile range. Now some truck manufacturers
say a DPF can last as long as 600,000
miles before cleaning. It's critical to understand
each asset in the fleet to really dial in the proper
maintenance schedule.
" If you've waited for the engine ECU to tell you
the DPF is dirty, you've waited too long, " said Ryan
Koukal, chief operating officer at CDS. That's why
CDS recommends cleaning every 100,000 miles,
or every year. On lower duty-cycle vehicles, CDS
recommends having the DPF cleaned every 1,000
miles. Koukal said more frequent cleanings
are worth it because a clogged DPF can lead to
reduced fuel mileage, additional ATS issues, and
downtime that can cost a fleet even more money.
february2022

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