December 2021 - 46

CASE STUDIES
Mining for the right data
Know what tests to perform on challenging vehicles to confirm your diagnosis.
By G. Jerry Truglia
E
veryday diagnosing and working
on vehicles is a challenge,
to say the least. Most days it's a
satisfying experience, but some days
are a nightmare. We all have those
days no matter how experienced,
well trained, and how good you think
you are. You're going to get your butt
kicked. Some vehicles just seemed
to be possessed, where nothing you
do goes right, or the vehicle still has
an issue.
2012 CHRYSLER
TOWN AND COUNTRY
The first nightmare was a 2012 Chrysler
Town and Country 3.6L van. The customer
complaint was that the vehicle
would sometimes stall, and the check
engine light would illuminate. My tech
Bill connected one of our scan tools to the
vehicle and came up with a P0480 " Cooling
Fan 1 Control Circuit/Open " . At first
glance it seems straightforward because it
is a common problem on many Chrysler
products. When the problem is intermittent
it becomes difficult to pull the
trigger on an expensive component (such
as a totally integrated power module or
TIPM), especially when an elderly woman
on a fixed income owns the vehicle.
To make sure the TIPM was bad we
had to test and not guess, so Bill put together
his game plan for how he was going to
proceed and test it. After many test drives,
he still had not uncovered the problem.
One of the first steps that Bill performed
was what I've taught in my class for years
-make sure the load is good by testing it
first. Bill did just that and applied voltage
and ground to the disconnected fan circuit.
He found that it worked as designed and
was not pulling excessive amperage.
His next step was to look at the wiring
diagram and hook up the eScope
to the terminals of the low cooling fan
relay (while the engine was cold). He
then monitored the signal as it warmed
up. With the scope connected and the
engine warmed up, the waveform confirmed
that the relay was not receiving the
command signal from the TIPM. There
was no ground path being provided for
the controlled side of the relay. Bill previously
confirmed all the necessary voltage
and ground supply as well as continuity
through the load. The conclusion of
his testing after multiple road tests (cool
downs and warm ups) confirmed that the
correct call was to condemn the TIPM.
He concluded that the TIPM's circuit
board couldn't complete the relay's path
to ground.
Bill made the right call because the
new TIPM confirmed the fix. With the
new part installed and the vehicle test
driven, all monitors turned " Ready " along
with the vehicle passing the NYS inspection
without a problem.
2013 DODGE DURANGO
Our next nightmare vehicle was a 2013
Dodge Durango 5.7L that had an illuminated
MIL and a P0750 " Low/Reverse
Solenoid Circuit " DTC. The vehicle was
stuck in 3rd gear via limp-home mode.
The first step was to review scan data
and freeze frame to see if the information
would shine further light on the problem.
Bill's next step was to consult our
service information. We used ALLDATA,
ProDemand, MotoLogic and Identifix to
see if there was any more information that
could assist his diagnosis. After researching
the different systems and reviewing
the wiring diagrams, Bill
located the
46 PTEN DECEMBER 2021 VehicleServicePros.com
correct pins and proceeded to perform
the recommended test.
The test that was recommended by
all the information systems specified a
resistance test that had to be measured
at the PCM connector. The specific resistance
specification for a good solenoid is
1.7 ohms. With the computer connector
removed Bill performed the test, finding
that all the solenoids measured 1.7 ohms
at the recommended temperature range.
Bill was perplexed by the test reading
he performed. He thought that one of the
solenoid readings would be different since
the computer was throwing a DTC and
was in limp mode. He shared the problem
with me and got me up to speed on the
test results. I am not a big fan of resistance
testing in most cases, and this was
one of those. I suggested to Bill to connect
an amp clamp and scope the current to
compare a good solenoid to the suspect
solenoid. The comparison game is a good
one to use since it is a direct comparison
between a good and suspect component.
Bill proceeded to reconnect the wire
harness connector to the computer so he
could start the engine up and test the current
draw of the solenoids. With two amp
clamps attached to the eScope, he came
up with the waveforms that told the whole
story. After we review the results, Bill was
still unsure if he should pull the trigger
on such an expensive part. The reason he
was thinking that way was that the recommended
resistance test passed. I reminded
him that the resistance test was not valid in
this case since the dynamic nature of the
current draw test revealed the solenoid was
drawing 19 amps.
He knew that he was the tech
who would be speaking to the customer
and had to make the correct
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December 2021

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