December 2022 - 12

TOOL BRIEFING
Parasitic battery drain is a bandit
The procedures to diagnose a battery drain can be time-consuming and tedious, especially
when an electronic module offers no clues to the events that occurred the night before.
By Roy Ripple, Contributing Editor
A
parasitic battery drain
is a bandit that creeps
in during the night and
kills your battery, sometimes
leaving behind no evidence of
the crime. The procedures to
diagnose a battery drain can be
time-consuming and tedious,
especially when an electronic
module offers no clues to the
events that occurred the night
before. Effectively utilizing the
proper diagnostic equipment
and a little ingenuity should lead
to a proper diagnosis.
With the doors closed and the key
removed, all modules in the vehicle should
enter sleep mode within seventy-five minutes
of shutting down. The current drain on
a battery should not exceed .050A once the
modules have turned off. Battery drains are
typically caused by a module that remains
awake or continues to wake up, sometimes
turning on other modules in the network.
The amount of time it takes a current
draw to kill a battery depends on the battery's
condition and the magnitude of the
draw. In most cases, a small drain under
1A will take a couple of days to discharge a
battery. A parasitic drain close to an amp or
higher will cause a quick overnight death.
DEAD FORD BATTERY
A 2015 Ford Fusion was towed to our shop
with a dead battery. The customer stated
that the battery died overnight. The first
thing we did was charge and test the battery.
It's essential that the battery is in
good condition and fully charged before
testing for a battery drain. I like to use an
easy-to-carry portable battery charger. I
hooked up my Dewalt DXAEC801B batp
An easy-to-carry battery charger is a great tool to have. This battery is at a 77 percent state of
charge, suitable for diagnosing a current draw.
tery charger and let the battery charge for
about two hours. My Midtronics EXP-890
battery load tester verified that the battery
was fully charged and in good condition.
After checking for aftermarket addons,
a common cause of a battery drain,
we took the vehicle on a road test. The
vehicle should be driven over 30 mph for
at least five minutes before testing for a
current draw. The idea is to turn things on
and wake things up. So, we activated everything
from the sunroof to the power seats.
MODULE TEST
After the road test, we checked all the modules
for Diagnostic Trouble Codes (DTC).
A faulty module or a module receiving a
bogus input can drain a battery, so DTCs
should be addressed before continuing
with battery drain diagnosis. I use the OBD
12 PTEN DECEMBER 2022 www.VehicleServicePros.com
Auto Doctor App on my phone when I need
to see what DTCs are in which modules. It
works fast and saves a lot of time. If there's
an issue, I use my OTC 3896 Evolve fullfunction
scan tool for diagnosis.
After we determined that there were no
DTCs in any modules, we needed to ensure
that nothing remained on once the vehicle
was shut down. We turned off the ignition
and exited the vehicle with the key, locking
the doors with the windows down. We
opened the hood and the trunk, engaging
the latches and disengaging the pin switches
so we could see the cargo lights go out.
We waited a couple of minutes until
everything shut off, looking closely at all
dash and instrument illumination. The
slightest glow in a touchscreen, a radio
knob, or a shift indicator is all it takes to kill
a battery overnight. Once we determined

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December 2022

Table of Contents for the Digital Edition of December 2022