Fleet Maintenance - 28

their hands on it to fully understand the training."
Littleton adds that OEM training can be helpful
for diagnosing one specific vehicle type, but for
technicians that work on various vehicle types,
a third-party trainer will typically focus more on
general technician improvement type training.
"That means it's not specific to one product line
- it's generic across all product lines, and teaches
them how to diagnose everything, not just one
specific way of doing it," he says.
"Train and evaluate technicians via real-time
Wi-Fi reporting to ensure all technicians are
following company repair procedures," Purkey
suggests. "Simply buying a tester is not enough.
Are your technicians using the tester? Are they
making the repairs as expected?"
He adds that even the best-trained technicians
will struggle with electrical diagnostics if they
do not have access to information on the systems
and diagnostic procedures on the equipment the
fleet is currently using. Every OEM and system is
different, and it is hard for technicians to diagnose
a system if they don't have the information on
how it is supposed to operate. Fleets should make
sure that technicians have access to accurate OEM
information and wiring diagrams, and that they
have the tools and equipment they need to effectively diagnose vehicles.
"Electrical diagnostics is the toughest task
a technician will ever face," says Steve White,
president of Electronic Specialties. "There are so
many different OEMs with different schematics, and that makes it particularly difficult to
stay abreast of all the nuances and changes that
happen almost daily. It's essential for techs to take
time to research the problem and the technical
information provided."

Common errors for misdiagnosis

Aside from a general lack of training or understanding of electrical systems, there are a few
common areas of confusion that can lead to
misdiagnosis.
* Voltage drop. One of the most commonly misunderstood diagnostic concepts in electrical diag-

ยป Fleets should make sure technicians have
access to the tools and equipment they need
to effectively diagnose electrical system issues
on vehicles.
Photo courtesy of Purkeys

nosis is voltage drop, says Purkeys' Rambeaux.
"You can have a wire that's damaged or corroded,
and if you put a voltmeter at the end with nothing
connected, you can see perfectly good voltage. But
as soon as you have a load on it, that voltage may
drop." When checking a wire or circuit, Rambeaux
stresses that technicians should be testing under
the same load that the wire is expected to handle
in normal operation. "If that wire in normal operation has to handle 5 amps, or 40 amps, or 100
amps, we need to put a load on it somewhat similar to that. So, circuits always need to be tested
under load, but you also have to make sure you
understand what that circuit should be loaded at."
* Relying too heavily on one measurement. A problem that Isuzu's Renno has noticed with inexperienced technicians is that they don't understand
how voltage, amps, and resistance work together
and only focus on one measurement - oftentimes
voltage. If a technician only focuses on one measurement, they are only seeing one-third of the picture.
If they use that limited information to make diagnostic decisions, they are more likely to misdiagnose
the issue, because they don't fully understand what
is happening in the electrical system.
* Not using the wiring diagram to inform the
diagnostic process. A wiring diagram is the tech-

nician's roadmap to figuring out electrical issues,
Renno says. "The biggest mistake I see technicians
make is they don't read a wiring diagram first.
They need to identify the circuit on the wiring
diagram, identify the points they need to check,
[and] decide what voltage, amperage, or resistance
they are checking there. Then when they go to the
truck, it's a yes or no answer." He adds that a lot
of technicians make the mistake of going to the
truck first, taking an arbitrary measurement, and
then going back to the wiring diagram to try to
find out whether the measurement was good or
bad. If they go to the wiring diagram first, they can
use strategy-based diagnostics to isolate the issue.
* Using static measurements instead of dynamic ones. Using test equipment in static situations
can allow technicians to misdiagnose circuitry
because it gives them a false sense that components are okay, says K&D Technical Innovations'
Littleton. When you take a dynamic measurement
while the circuit is operating, you get a true idea
of what is happening in that system. "One thing
that some technicians miss the boat on is they
avoid checking things dynamically, because in
electrical systems, everything is connected, and
they believe that to attach themselves in a circuit
in a way that sometimes could cause damage to
the circuit. A lot of technicians don't understand
that you can do things inductively with an amp
probe where you can go around the outside of a
wire with an amp probe without being intrusive
in the circuit," Littleton explains.
* Relying too much on OEM software and scan
tools. "Some technicians tend to rely on the OEM
software and the scan tools to figure out root causes of problems," Littleton says. "A lot of times, root
causes are found by testing dynamically, not by
looking at a scan tool or looking at software. You
can't just plug in the scan tool into the truck and
expect it to say, 'Go to connector number three,
there's a high resistance there.'"
* Assuming the wiring harness is okay. "Most
diagnostic procedures assume that the wiring
harness is okay," Renno says. "That's where technicians can get tripped up and go through the
service procedure and replace a lot of parts, and

Tips and tricks for reading wiring diagrams
Industry experts offer their tips for getting
the most out of wiring diagrams.
When looking at a wiring diagram,
don't try to focus on the whole
page all at once. It's overwhelming. Put a blank sheet of paper
next to the wiring diagram and
just draw the simple circuit. Focus
on the simple part and follow
the current flow from power to
ground or from ground to power.
All complex wiring diagrams are
just a series of simple diagrams,
and it makes it hard to look at
if you don't narrow down to
the circuit that you're doing.
-John Renno, Manager, Center of
Excellence, Isuzu Commercial Trucks

28 Fleet Maintenance | July 2019

Print the wiring diagram off and
use highlighters to trace the
circuit. When you use your finger
or follow the circuit with your
eyes, it's easy to mistrace the
circuit. One trick that I use is to
print the same wiring diagram
off twice. On one, I'll trace the
current flow, how it operates,
and that shows me what parts
of the circuit I need to check.
Then on the other one, I'll start
coloring the things that tested
okay. When I get done, anything
that's not highlighted are suspect
circuits that I need to identify.
-Keith Littleton, Trainer and Owner,
K&D Technical Innovations

To properly read a wiring diagram, one has to know how
the components in the system
operate. For example, if a module
is powered up and it sends out a
signal of half the voltage and the
technician does not know this,
he would think he has a problem,
as he would expect a 12V signal.
Following diagrams is fairly simple, but using it within the scope
of how the system operates is a
different matter. My best advice
is not only look at the diagram,
but understand how the components operate when in use.
-Bruce Purkey, Founder of
Purkeys and consultant for
Auto Meter Products

Read wiring diagrams from negative to positive and redraw the
circuit as a straight line. All circuits
are the same - voltage, ground,
single component, and switches.
-Steve White, President,
Electronic Specialties

Before reading a schematic, get
familiar and understand all the
symbols. Read the schematic
like a roadmap. I print the schematic and highlight the circuit
I'm diagnosing to make sure
I'm staying on the right path.
-Gerald Tabas, ASE Master
Technician, Power Probe Tek



Fleet Maintenance

Table of Contents for the Digital Edition of Fleet Maintenance

Uptime - How you can make the most out of your shop's ROs
Foundation for success: How do you find and keep technician talent?
Vehicles - Examining the e-systems available for today's fleets
In the Bay - Do techs understand the fundamentals of electrical system diagnosis?
Shop Operations - How to assess replacement parts
Reman, Rebuild, Replace - Reasons fleets should consider reman
Economic Outlook - Uncertainties with today's global economy
Tire Tactics - Factors to help determine the lifecycle of tires
Management - The "shop improvement" conundrum
Fleet Parts & Components
Tools & Equipment
Classifieds
Guest Editorial - Increase shop efficiencies through fluid management
Fleet Maintenance - 1
Fleet Maintenance - 2
Fleet Maintenance - 3
Fleet Maintenance - 4
Fleet Maintenance - 5
Fleet Maintenance - 6
Fleet Maintenance - 7
Fleet Maintenance - Uptime - How you can make the most out of your shop's ROs
Fleet Maintenance - 9
Fleet Maintenance - Foundation for success: How do you find and keep technician talent?
Fleet Maintenance - 11
Fleet Maintenance - 12
Fleet Maintenance - 13
Fleet Maintenance - 14
Fleet Maintenance - 15
Fleet Maintenance - 16
Fleet Maintenance - 17
Fleet Maintenance - Vehicles - Examining the e-systems available for today's fleets
Fleet Maintenance - 19
Fleet Maintenance - 20
Fleet Maintenance - 21
Fleet Maintenance - 22
Fleet Maintenance - 23
Fleet Maintenance - In the Bay - Do techs understand the fundamentals of electrical system diagnosis?
Fleet Maintenance - 25
Fleet Maintenance - 26
Fleet Maintenance - 27
Fleet Maintenance - 28
Fleet Maintenance - 29
Fleet Maintenance - Shop Operations - How to assess replacement parts
Fleet Maintenance - 31
Fleet Maintenance - 32
Fleet Maintenance - 33
Fleet Maintenance - 34
Fleet Maintenance - 35
Fleet Maintenance - Reman, Rebuild, Replace - Reasons fleets should consider reman
Fleet Maintenance - 37
Fleet Maintenance - Economic Outlook - Uncertainties with today's global economy
Fleet Maintenance - 39
Fleet Maintenance - Tire Tactics - Factors to help determine the lifecycle of tires
Fleet Maintenance - 41
Fleet Maintenance - 42
Fleet Maintenance - 43
Fleet Maintenance - 44
Fleet Maintenance - 45
Fleet Maintenance - 46
Fleet Maintenance - 47
Fleet Maintenance - 48
Fleet Maintenance - 49
Fleet Maintenance - 50
Fleet Maintenance - 51
Fleet Maintenance - 52
Fleet Maintenance - 53
Fleet Maintenance - Management - The "shop improvement" conundrum
Fleet Maintenance - Fleet Parts & Components
Fleet Maintenance - 56
Fleet Maintenance - 57
Fleet Maintenance - Tools & Equipment
Fleet Maintenance - 59
Fleet Maintenance - 60
Fleet Maintenance - Classifieds
Fleet Maintenance - Guest Editorial - Increase shop efficiencies through fluid management
Fleet Maintenance - 63
Fleet Maintenance - 64
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