Fleet Maintenance - 26
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Bruce Purkey, founder and chief creative
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"Roadside breakdowns and unnecessary repair expenses can result from
misdiagnosis," Purkey stresses.
In addition, when technicians replace
parts that don't need to be replaced in
an attempt to further their diagnosis, it
can make it more complicated to isolate
the root cause of the issue, adds Keith
Littleton, trainer and owner of K&D
Technical Innovations. Littleton has
worked in the industry as a trainer and
technician for over 30 years.
"Going down the wrong path of misdiagnosis starts this kind of evolving situation
that makes it really difficult to diagnose
the root problem because you never really
know where the issue started from," says
Littleton. "A lot of times, technicians are
missing really small things. Probably 65
to 70 percent of the time, it's very basic
problems that get overlooked, and many
parts get replaced that aren't necessary."
Ensuring that technicians have the
correct tools to diagnose a vehicle, the
know-how to use their tools correctly, and
have training to effectively diagnose an
electrical problem can help minimize
misdiagnosis issues and maximize vehicle uptime.
The basics of
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26 Fleet Maintenance | July 2019
Gerald Tabas, ASE Master Technician
for Power Probe Tek, compares a vehicle
electrical system to the human body's
"The battery is the heart of the vehicle," he explains, and "wiring runs like
veins, allowing voltage to travel to various parts of the vehicle, such as switches
Like blood flowing from the heart to
the rest of the body, electrical current
flows under pressure to the various
components being powered-this
pressure is measured in volts. The
total strength of the electric current is
measured in amperes, often shortened to
amps. As electricity flows, it encounters
resistance, which is measured in ohms.
These three measurements of electricity - voltage, amps, and resistance - are
a key part of understanding electrical
system diagnosis, explains Isuzu's Renno.
"If you can understand those three
components together, you can do very
well at diagnostics. If you can figure out
two of those measurements, you can
understand all three. If you know the
voltage and amperage, you can figure out
the resistance, or if you know the voltage and the resistance, you can figure out
what the amperage is doing."
Nine essential aspects of vehicle
electrical system diagnosis
* The time for diagnostics and repair in the mechanical and electrical worlds
are flipped. A mechanical diagnosis is fast, but the repair can take hours;
an electrical diagnosis can take hours, while the eventual repair is usually
quick - sometimes only minutes. It's important for the shop supervisor and
the tech to understand this so that the process can be managed properly.
* There's no such thing as an electrical "repair." Once the actual fault is discovered, the electrical process ends, and the mechanical begins. Even if
the fault is a shorted or broken wire, the repair is fully mechanical. When
the diagnostic tools are put down and the repair tools are picked up, the
process is mechanical. The only "electrical" process is the diagnosis.
* Nearly all electrical faults are simple, and 80 percent of all faults occur within the circuit. Often, a vehicle can be shut down and disabled by a fault
that is entirely invisible to the naked eye. Small amounts of corrosion in
any circuit can cause total failure. Oxidation only 0.001" thick on a single
pin of one connector will fully destroy system operation, and in the wrong
system, this fault will cause a 400-ton truck to stop dead in its tracks.
* Voltage drop is an effective diagnostic measurement. Voltage drop requires
the circuit to be functioning, or complete, but if done properly, the test
cannot fail. OEMs frequently specify a resistance or ohm reading, but
these tests can be time-consuming, complicated, and inconclusive.
* The ohmmeter is prone to failure. The standard ohmmeter function in a digital
multimeter is only designed to work within a small region of a very small system.
Larger vehicles have extensive wiring harnesses, and the small amount of voltage
used by an ohmmeter might not have enough energy to complete a definitive test.
* Many electrical tools are not fully effective for many circumstances. A test light is an
age-old tool that most technicians either have seen or still have - even though there
are more effective options. If the tool has electronic, solid state components, test
lights are likely to miss a blatant fault because they aren't sensitive enough. An older
incandescent bulb tool can also damage sensitive electronic systems on vehicles.
* Schematics are often hard to acquire, and more often read incorrectly. A
schematic is an illustration of circuits, and circuits comprise systems. When
reading a schematic, it must beread for understanding then redrawn as a
straight line. Additionally, it should be read from negative (-) to positive (+).
* All circuits are the same. Every circuit contains four essential parts - a voltage supply (+), a ground return path (-), a SINGLE load component, and
switches. Even if this isn't plainly illustrated by the OEM in the schematic,
this is what is there, and this is what the tech should look for when reading. If you know this one principle, you understand every circuit.
* All "advanced" electrical systems are based upon, and work according to, old and
well-understood concepts. No "modern" electrical system is truly new - electrical sensors, electrical vehicles, and all computers work according to basic
principles. This suggests that all training should begin with the core components
of electrical theory, and advanced training should always include these principles. "Ohm's Law" governs nearly all circuits and systems in a vehicle. Ignoring
these lessons doesn't speed up training and diagnostics - it slows it down.
Information provided by Electronic Specialties
"One of the most important starting
points for technician training is to go back
to the basics, and for electrical diagnostics, part of that is simply training technicians how to use a multimeter," says Larry
Rambeaux, sales manager for Purkeys.
He notes many managers that contact
him for training believe their technicians are ready for an advanced course
in electrical work and are above average. He cites one example where a fleet
was adamant that its technicians were
too advanced for what Rambeaux calls
"Multimeter 101." But, when given a
pre-test to gauge the technicians' actual
skill level, the fleet was shocked by how
low the scores were.
This is a common issue, Rambeaux
says. Last year at the TMC SuperTech
technician skills competition, of the
top 116 technicians that competed, the
average score was only 66 percent. "There
is plenty of room for improvement," he
An alternative to subjectively judging
technician skill level based on limited
observation is to have technicians take
standardized tests. There are a variety
of standardized tests available - the
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
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