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ESSENTIAL TOOLS

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data is just that. Without the understanding of system-configuration (all the
players involved in carrying out a specific
goal or output), there would be no understanding of which data PIDs were necessary to view. The decision about which of
the PIDs to display will be derived from
the information found by referencing a
wiring diagram as well as the description
and operation of the system. These PIDs
will represent:
Inputs: Information about individual
components' physical state (pressure,
temperature, angle, or position) and the
intent of the ECU or person operating
the system.
Decision making: This information,
or processed data, is reflected by the ECU
PIDs and indicates a state of operation (a
" thumbs-up " or " thumbs-down, " if you
will). They will typically be displayed
as " on/off, " " yes/no, " " permitted/notpermitted, " etc. This gives us, as technicians, valuable insight.
Shared data: Many systems exist on
a virtual platform, meaning their functionality requires a communication bus
(or several) with integrity. If data that is
being processed in a specific node is then
reflected in the PID list of another node,
this is a good indicator that the data is

16 I Diagnostic Process I December 2020

being shared over the network. This provides for a means to split the system into
sections in which to troubleshoot. With
a little common sense and knowledge of
the previously researched system, a lot
of unnecessary testing will be avoided.
Outputs: This is the result. Thinking
in terms of a true " system, " any breakdown in the above-mentioned will not
allow for an output to occur. Seeing the
entire story reflected in the scan tool list
will show your intent to operate a system,
the data required for an ECU to make a
decision, and the final decision to operate
or not to operate a component (and the
reason why). Ask yourself, would you be
thinking about testing a switched input
(like a window switch) if the scan tool
reflected a PID that showed the intent
to lower the window?
One of the most valuable times to
employ the scan tool is during drivability
analysis. Just think of how situations can
yield a " low-power " complaint. Inputs/
processing/outputs ... it's the same for
drivability. We typically reference the
fuel trim values to reflect how well the
engine is being fueled. This is the end
result or feedback. When a vehicle fails
to produce power, it's because the engine
can't breathe properly, the air/fuel ratio

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is incorrect, or the ignition timing is not
as it should be (or it is inadequate). With
a properly set up PID list (in a graphed
format) and running the engine under
different operating conditions, it's easy
to determine the cause of the low-power
complaint right from the driver's seat.
Considering all this data is gathered
right from the driver's seat, I can't think
of a more efficient way to begin a diagnostic approach.
For each vehicle that rolls into the
bay, your scan tool can open your eyes to
how all the players function together to
carry out a goal. You get to see the entire
story play out for you, so diagnostic direction can be gained before investing time
in a specific area. Begin employing these
capturing/analysis techniques on wellknown vehicles and get comfortable with
the functionality of your specific scan
tool(s). Learn the ins and outs of it and
what makes it special. You do that and
watch how quickly productivity and confidence soar in the shop.
Brandon Steckler is Technical
Editor of Motor Age. He is a
working technician at Lykon
Automotive in Bristol, Pennsylvania.
He has worked in the field for over
18 years and holds multiple
ASE certifications.

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