Fleet Maintenance - 35

things at the same time. You're checking the position
sensor to make sure it is functioning properly, but
you're also checking the motor to make sure it isn't
requiring more voltage to operate, which would indicate that there's resistance. Quite simply, a scope can
allow a technician to see things a scan tool can't see."
In other instances, an oscilloscope can make existing processes a lot more efficient.
"Take a relative compression test where a technician checks the balance between each cylinder
on an engine," Carnes says. "Some manufacturers
have this built into their software, but some do not.
When they don't, a technician has to start pulling
an engine apart to visually inspect for mechanical
issues. When using an oscilloscope, a technician can
get the information he or she needs in a lot less time,
probably three or four hours less."
There are also instances where a scope is simply a
better tool than what is normally being used.
"If you think about the CAN bus J1939 where data
is moving at 250 to 500 kilobytes per second, a multimeter cannot keep up and provide the information
the technician needs," Carnes explains.
When that happens, the multimeter might diagnose some intermittent issues. Sometimes a truck
comes in with inactive fault codes. The multimeter
can't see anything that's wrong.
"That's where you could hook up an oscilloscope to
analyze the sine waves coming from those modules,
which can help pinpoint things that don't look right,"
Carnes adds.

Getting started with
scope diagnostics

To begin taking advantage of scope diagnostics,
Carnes says most fleets are looking to modern digital
storage oscilloscopes. The scope itself has leads on

»An example of a sine wave captured by Diesel
Laptops' new oscilloscope, The Diesel Scope.
Image courtesy of Diesel Laptops

»Diesel Laptops is in the
process of introducing
its new oscilloscope for
the heavy duty market,
The Diesel Scope.
Photo courtesy of Diesel Laptops

it similar to a multimeter. The scope also has a USB
cable that connects to a laptop or tablet. Software
collects all of the data so the technician can view
and analyze it.
"The hardware [scope] goes directly to a sensor or
module on a truck," Carnes explains. "The technician
hooks it up directly by either back probing the sensors
or using breakout harnesses or amperage clamps,
depending on what the tech is doing. The most difficult part of getting into scope diagnostics is knowing
where to hook up the tool to get the right readings."
That is why supplier support is so critical. A good
supplier will not only provide a good tool, but also
training and support so the technician can make
the most of their new scope.
Freeman says there are a handful of oscilloscopes
geared toward the heavy duty market. Some are
rather high-end with a price tag as high as $10,000.
Autel's scope, the MaxiScope MP408, is designed
for a technician who is just getting started with
scope diagnostics.
An example of useful, high-end functionality is the
ability to stack sine waves. Think back to the earlier
example of trying to diagnose whether an EGR issue
was sensor-related or the EGR itself.
"With a high-end oscilloscope, you can monitor
movement of the EGR position sensor and the actuator itself," Freeman says. "You can record both,
and then overlay the sine waves to see if the sensor
matches up with the actuator. If they don't match
up, you know the sensor is bad."
Another example of high-end scope functionality
has to do with something called packet descriptions.
Freeman likens that to name tags for ECMs.
"When you connect an oscilloscope to a vehicle
with multiple ECMs, there are a lot of sine waves
coming back to you," Freeman explains. "With a scan
tool, you also get a lot of different information on
a lot of different systems. But with a scan tool, the
information is populated and labeled. Not
all oscilloscopes do that. A high-end scope
will, which helps the technician know
what he or she is looking at."
Like most new technologies, scope diagnostics is not something most technicians
can learn overnight.
"It takes a bit of time to understand what
you are looking at, such as sine waves,"
Carnes says. "Fleets shouldn't think that a
technician will suddenly get a truck done
in an hour on the first day after purchasing
an oscilloscope. That said, once the technician becomes proficient with it, there is
almost nothing that comes into the bay
that the tool can't be used on. If a truck shows up
that the technician has never worked on in their life,
the technician can use the scope to start probing to
see how the electrical system works."
From there, the technician can also identify
electrical issues a lot faster. That means faster
repairs and less downtime, which is a goal for
all fleets.
"I firmly believe that the ability to do scope
diagnostics is what will separate one level
of heavy duty technicians from the other,"
Freeman says. "With the complexity of the
heavy duty truck changing so fast, this
expertise is going to be very valuable
going forward."

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Fleet Maintenance

Table of Contents for the Digital Edition of Fleet Maintenance