Diagnostic_Process_Guide - 14

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14 I Diagnostic Process I December 2020

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proved that the suspect solenoid circuit
did not produce a healthy inductive kick
like that of a healthy solenoid circuit. It
also displayed that the ground side of the
circuit was compromised and the PCM
was likely at fault. This conclusion was
made because the ground path still had
significant voltage available on it when
energized. That, coupled with the fact
that we tested directly at the PCM terminal, concluded that wiring was not
an issue. If the PCM's ground was compromised, the other solenoids' circuits
would've suffered as well.
The only logical explanation was a
poorly functioning solenoid driver within the PCM itself. To further prove the
fault, I continued to monitor the suspect
circuit. This time, I supplied an external ground which allowed me to bypass
the PCM. This enabled the solenoid to
function properly and resulted in a voltage signature that pulled very close to the
ground and an inductive kick, similar to
the known-good solenoid when the circuit was de-energized. I followed the
above test with a measure for current
flow from each of the solenoids using the
lab scope and a low-amp probe. Seeing

that they all drew about the same amperage reassured me that the failed PCM
driver had nothing to do with a shorted
solenoid-winding.
Being an efficient and accurate diagnostician isn't about having the fastest
hands in the shop. It's more about using
logic. Having fundamental knowledge
built from mastering the basics and
learning to utilize the tools you have
comes from practicing on known-good
vehicles and investing your free time
to better yourself. Take time away from
the vehicle to develop a diagnostic game
plan derived from the goodies provided
by service information. A combination
of the wiring diagram and description/
operation will yield you the arsenal you
need to combat the vehicle and win the
battle. It all starts with a little discipline
and patience, but it ends with the rewarding feeling of a job well-done.
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.
http://www.AUTEL.COM/ULTRA http://www.VehicleServicePros.com/21075591 http://www.VehicleServicePros.com/21131406 http://www.VehicleServicePros.com/ http://www.VehicleServicePros.com/10095724
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