Download proven techniques battery drain diagnosis proven

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T
hanks to modern technology,
battery drain diagnosis is
more difficult than it used to
be, and I could devote page
upon page to the topic. But
here I’ll concentrate on areas
that seem to be totally overlooked or else
badly misunderstood. My field experience
has been that some technicians are both
well-read and well-equipped for these tasks.
But others struggle because they’re steeped
in outdated methods and/or careless shortcuts. For instance, many guys disconnect
batteries without considering the consequences. Others still try to gauge key-off
drain with test lights. I frequently meet
techs who have never used a door switch
“closer” or a battery drain test switch.
No, this is not your father’s battery drain
diagnosis. Sure, some basic steps are ones you
may already know; and some steps apply to
all vehicles. But you must evaluate each vehicle individually to judge the most efficient
way to measure key-off battery drain. One
single technique isn’t fast and easy on every
single car. Component access may weigh
heavily in your decision. The bitter fact is that
component access on many vehicles falls
somewhere between horrible and terrible.
Take Control of the Job
When I was a teenager, older mechanics
taught me a basic routine that diagnosed
99% of the battery drain complaints. I
checked the car’s dome light first. If it was
off, then I looked for courtesy lights inside
the glove box, console, trunk and engine
compartment. If a bulb was hot the moment after I opened the glove box, trunk,
etc., then the switch controlling that bulb
was stuck closed (shorted). Fortunately,
these same checks are still as useful now as
they were in the late 1960s.
Today, however, there are many more
possible causes of excessive battery drain.
What’s more, the cost of a bungled diagnosis is considerably more than a trunk switch
R&R. That’s why I urge you to take control
of the job and maintain control until you fix
the vehicle. This testing takes time and
knowledge; not every motorist is willing to
pay for that time and knowledge—period!
The first step to controlling the job is
establishing an initial diagnostic fee. You
don’t have to do this, but experience
shows that battery drain jobs can just devour time. Anyway, where necessary, explain the critical steps you must take
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PROVEN
TECHNIQUES
FOR
BATTERY DRAIN
DIAGNOSIS
BY DAN MARINUCCI
Modern technology has complicated
battery drain diagnosis. A careful,
methodical approach always pinpoints
more problems, more often, than
guesswork and false assumptions.
first—for example, thoroughly testing the
battery and charging system. Next, you
must wait for the on-board electronics to
go to sleep and then measure key-off current. What’s more, you may need to research the vehicle and its systems. You
easily could burn 60 minutes or more researching a battery drain issue.
Meanwhile, reassure the customer that
you’ll update him on the job as it progresses. If pinpointing the problem is
easy, you have the option of reducing the
diagnostic fee. Intermittent or elusive battery drains require more test time, and
that means more money. Some battery
drains can be maddeningly random.
Vehicle History Is Vital
For now, suppose that you secured a diagnostic fee. The next step is gathering the
vehicle’s history. Some people think this is
a nuisance. But the sharper the information the customer provides, the greater
the chances of your diagnosing the problem quickly.
Okay, the driver shuts off the ignition
switch and then the battery discharges.
When did this symptom first appear? Did
it occur only after someone worked on the
vehicle? If so, then who worked on it and
what did he do? Based on the work that
was done, do any potential battery drain
issues jump out at you?
Did someone replace the battery? If so,
is it a high-quality battery with the proper
reserve capacity for the application? The
time it takes the battery to discharge may
be a useful clue as well. For example, a battery that dies within a few hours suggests a
relatively high-current drain. But suppose
the battery dies only when the vehicle sits
undriven for a week, in an airport parking
garage, for instance. In that case, the battery itself may be the culprit. The battery
could be failing or it may be a replacement
item with inadequate reserve capacity. (I’ll
return to batteries momentarily.)
Did someone install accessories? To
me, it doesn’t matter whether a car dealer
tech, an independent tech or do-it-
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Photoillustration: Harold A. Perry; images: Electronics Specialties, Exide Technologies & Thinkstock
A Fault and Battery?
yourselfer installed accessories. If the only
change to the vehicle was that installation,
then I’m suspicious of the product itself as
well as the details of the electrical hookup.
For all you know, a recently installed car
alarm, sound system or remote-start setup
could be a key-off power hog. Or, the
product itself may be fine but the installer
bungled the electrical hookup. (Readers,
can you say hot all the time?)
The point is that the diagnosis may
amount to inspecting the last place human
hands touched the vehicle. Also, listen
closely to the customer. Don’t disregard or
underestimate things people tell you about
their vehicles and driving experiences. Instead, try to correlate the discharged battery to the driver’s usage and habits.
For example, parking on a hill could be
relevant. The mercury switch used to be a
common method of operating a trunk
light. Sometimes a failing mercury switch
would short out only when the vehicle was
parked on a hill at just the proper angle.
Changing drivers or jobs may be clues.
For example, suppose a vehicle’s battery
already was in marginal condition. Or
someone installed a replacement battery
with insufficient reserve capacity. Neither
of these conditions may have been an issue until the owner started a new job and
began leaving the car at an airport for a
week at a time, or one of his kids borrowed it and then parked it for a week.
Watch for OEM features such as remote entry and remote start. These systems, which affect battery drain, have become topics unto themselves. You’ll find a
neat summation of them in Karl Seyfert’s
Trouble Shooter columns of January and
February 2011. Ultimately, you may have
to verify that these systems are working
normally and that the drivers are using
these features correctly.
Finally, check all your sources for relevant service bulletins. Some service managers and technicians also routinely visit
OEM websites in case there’s recent
news that hasn’t reached aftermarket
channels yet.
Battery maintenance and capacity are other details you must not underestimate.
First, batteries don’t require as much maintenance as they did years ago. Second, a
damp, dirty battery case ultimately may
cause a battery drain. Third, electrical specialists have warned me about this issue;
they claim that batteries still don’t get the
maintenance they deserve. Fourth, many
techs totally ignore battery maintenance.
Obviously, underhood components
such as batteries eventually get dirty
and/or wet. Eventually, dirt on top of the
battery may conduct current, discharging
the battery. If you doubt this, get a digital
multimeter with a milliamp (mA) scale.
Hold one of its test leads on the positive
battery terminal, then touch the other
lead to various points on a damp, dirty
battery case. If the meter shows that current is flowing, then that battery is discharging while you’re watching it! Clean it
and dry that battery.
Be sure the battery has the correct reserve capacity (RC). Certainly, this isn’t a
potential problem in every instance of a
dead battery. However, RC has become
more and more important on modern vehicles. Furthermore, countless techs I’ve
met don’t know what RC is or why it may
affect battery drain diagnosis.
By definition, reserve capacity is the
length of time in minutes a battery can
supply 25A while maintaining a voltage of
10.50V. Remember that RC is measured
on a new, fully charged battery at 80°F.
(Think about that: The battery is pumping
out a steady 25A until its voltage drops to
10.50V!) Engineers boost RC by putting
thicker plates in the battery.
To grossly simplify, RC does two things:
First, it powers the ignition system and
vehicle lighting if the alternator fails. Second, it powers electronic components that
draw current after the driver shuts off the
ignition switch. Generally speaking, the
greater the number of these components,
the greater the RC rating is likely to be
and the more important the rating becomes. What’s more, the longer the customer parks his vehicle, the more important RC becomes. Arguably, the rating is
less critical on a vehicle that’s driven daily.
You can connive, compute and contrive
ways to circumvent or shortchange an automaker’s RC rating. Remember, shortcuts are never a problem until they cause
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PROVEN TECHNIQUES FOR BATTERY DRAIN DIAGNOSIS
should be listed in the electrical section of a
good shop manual or other service literature. However, the situation is more complicated on replacement batteries. For example, the RC rating may appear on a battery manufacturer’s replacement products.
But when that battery is private-branded,
the label may not show the RC rating. Sim-
ilarly, some battery catalogs list RC ratings
and others don’t. So in some instances,
you’re at the mercy of the battery vendor.
Planning Your Work
Carefully planning the procedure is another aspect of controlling the job. Failing
to do so can cost you a bundle! Your initial
Photos: Dan Marinucci
a problem. Cover your rear end—not to
mention the shop’s reputation—by installing a replacement battery with the
proper, specified reserve capacity.
The typical RC ratings on automotive
batteries range from 70 to 150 minutes.
Usually, the label on an OEM battery
shows the specified RC. What’s more, RC
Normal parasitic battery drain usually
measures approximately 30 to 50mA.
A milliamp scale is more sensitive than
a regular amps scale. It also saves you
the trouble of figuring out the decimal
point placement!
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September 2014
goals here are twofold: First, allow the onboard electronics to time out. Depending
on the vehicle and its systems, waiting for
sleep mode could take anywhere from 35
minutes to several hours.
Second, measure key-off current after all
the electronic components are asleep.
Many techs call key-off current the parasitic
drain. Some check parasitic drain directly at
the battery with a digital ammeter and a
test switch. Others do it by clipping an inductive current clamp around a battery cable. If the drain is excessive, the most common way of isolating the cause is removing
one fuse at a time. If the current drops to
normal when you remove a fuse, then that
fuse identifies the offending circuit.
If you’re using these methods, then
hopefully the battery is under the hood
and easy to reach. You may have to remove ductwork and/or brackets to access
the battery. Occasionally you have to remove the hold-down and carefully slide
the battery a little bit one way or the other
to create some working room.
Of course, the battery may be under
the rear seat or rear floor. It also could be
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PROVEN TECHNIQUES FOR BATTERY DRAIN DIAGNOSIS
hidden in the trunk or cargo area. Sensible service managers make customers remove their personal junk from the vehicle
beforehand so techs don’t waste time removing and storing it. Plus, you may have
to find a safe, clean place to stow such
items as a rear seat cushion, an interior
panel or interior trim pieces.
Yes, these two initial steps require a secure place where the customer’s vehicle
can sit undisturbed for up to several
hours—with the hood, trunk, rear hatch
and/or a door wide open. At some shops,
bays are kept open specifically for these
kinds of tasks. But at other garages, space
is at a premium. In those cases, schedul-
ing wisely and working smart are doubly
important.
Smart technicians also anticipate the
chores of finding fuses and closing door
switches. Typically, you’ll be touching the
fuses at some point during battery drain diagnosis. Pay attention because many vehicles have more than one fuse panel. Also,
Basically, reserve capacity (RC) is how
long (in minutes) the battery can support the vehicle’s ignition and lights if
the alternator fails. But RC is also important for supporting normal key-off
current draw. Use of thicker battery
plates increases the RC rating.
Circle #32
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September 2014
the fuse panel(s) may or may not be readily
accessible. And the fuse you’re seeking
may not be located where you assumed it
would. Finally, the fuses may not be technician-friendly, another detail I’ll cover later.
Dealing with door, trunk or hatch
switches is vital to your battery drain diagnosis. Obviously, you have to open the vehicle in order to reach the battery and/or
fuse panel(s). The moment you do, one of
the above-mentioned switches turns on
the interior lighting and wakes up vehicle
networks. This causes an erroneous parasitic drain.
For years, I’ve used Thexton’s tools
(www.thexton.com) to close door switches. Tool No. 442 handles door switches on
the A-pillar and No. 445 handles switches
on the B-pillar. When the door switch is
hidden inside the door latch, carefully inserting a tool in the latch should close the
switch. Several common things may work
here—a stubby screwdriver, a short
punch, etc. Just take care to remove the
tool and operate the door handle before
trying to close the door again.
Forewarned is forearmed: There could
be cases where you’ll have to access a
switch and figure out how to close it or
perhaps bypass it with a jumper wire.
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PROVEN TECHNIQUES FOR BATTERY DRAIN DIAGNOSIS
Test Precautions
Let me stress three important points, all
borne of experience. First and foremost,
recognize normal parasitic drain values.
Sometimes these aren’t published or
they’re very difficult to find. Key-off current on a healthy vehicle is usually—typically—within the range of 30 to 50mA.
That’s equal to .030 to .050A. Try building
your own personal database by faithfully
recording both known-good and knownbad parasitic drain numbers. What’s more,
maintain solid working relationships with
competent dealer techs who are making
the same measurements.
Second, keep your perspective on bat-
Circle #33
tery drains. If a vehicle has a legitimate
problem, you could encounter parasitic
drains in the 90- to 100mA range, for instance. However, the vast majority of parasitic drains that cause customer complaints are substantially greater than
those. Usually the difference between a
normal parasitic drain and one that’s
killing the battery is significant—not just a
difference of 40 to 50mA.
Third, avoid disconnecting the battery.
Obviously, doing this shuts down everything in the vehicle. Experience repeatedly has shown that the cause of an excessive drain may not come back when you
reconnect the battery. Instead, it may take
weeks or months of driving for the condition to reappear! What’s more, this isn’t a
problem associated with just the newest
vehicles. To the contrary; I recall field service engineers warning me about “battery
disconnect” as far back as 1990.
Okay, what if you do have to disconnect
a battery? (A common reason is to install a
test switch.) Then road-test the vehicle after you reconnect the battery, operating as
many electrical accessories as practically
possible. With a little luck, the cause of
the excessive drain usually returns.
And there’s a fourth point: Don’t disturb a vehicle or its systems in any way
when waiting for sleep mode. In particular, keep all remote-entry fobs far away
from the vehicle.
Direct Current Measurement
Circle #34
Circle #36
Circle #35
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September 2014
Using a test switch and digital ammeter is
the simplest, most accurate way to measure parasitic drain directly. A test switch
goes between the negative battery terminal and negative battery cable. The photo
on page 54 (top center) shows the most
common style of test switch. Tightening
the green knob closes the switch; loosening the knob opens it. Tool suppliers such
as OTC (www.otctools.com), Thexton and
others offer test switches. You’ll also find
them on the internet.
The plan here is to install the test
switch, close it and then restart the engine. Road-test the vehicle and operate as
many accessories as practically possible.
Then park it in the bay assigned to this
job. Create access to the areas of the vehicle where you’ll need to work. Then do
what’s necessary to close the door or rear
hatch switches. Next, wait for the vehicle’s
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PROVEN TECHNIQUES FOR BATTERY DRAIN DIAGNOSIS
These long, blue fuse assemblies on late-model Toyotas are
an example of a fuse that you can’t probe and voltage drop—
its terminals are covered. Plus, the single assembly protects
or “fuses” several different circuits simultaneously.
Using a fused test lead is an old but cheap, effective way to
add another level of protection to that valuable multimeter.
Replacing a blown standard fuse in the test lead is cheaper
and quicker than replacing fuses inside the multimeter.
electronics to go to sleep. Pass the time by working on other cars.
Fetch a digital multimeter that measures current—preferably
one with fused amps and milliamp scales. (A number of professional-grade multimeters feature a fused 10A as well as milliamp
scales.) Select the 10A scale or the highest current scale the meter has. Connect the meter across the test switch and then open
the switch. Now whatever key-off current is present has to flow
through the meter. This format yields the most accurate parasitic
drain measurement. Yes indeed, squeezing a test switch into a
cramped engine compartment can be a hassle—but usually
worth it. Sometimes you may have to improvise good connections when installing a test switch.
If your meter has a milliamp scale, use it whenever possible because it’s a more sensitive scale. Imagine that the initial ammeter
reading, captured on the 10A scale, was .365A (365mA). If the meter’s milliamp scale goes up to 500mA, then you can safely measure 365mA with it. So, close the test switch at the battery, select
your meter’s milliamp scale and then open the test switch again.
Remember that a proper test switch can handle starter current. So it enables you to restart the engine. Restarting the engine and operating accessories has been vital to recreating the
battery drain conditions that we’re trying to diagnose. You can’t
restart the engine when using some battery drain test methods,
including a test light.
Indirect Current Measurements
There are two ways to measure parasitic drain indirectly. The first
is the inductive current clamp method; the other is checking voltage drop across each fuse. Let’s look at the inductive clamps first.
Over the years, I’ve been using a variety of inductive current
clamps (sometimes called probes) for assorted electrical tests. I’m
convinced these clamps have great value. But you have to choose
the product very carefully—one size doesn’t fit all. Wherever possible, try out the clamp before buying it.
The challenge here is finding an inductive tool that meets two criteria. First, its clamp has to be large enough to fit around common
battery cables. Second, it has to be sensitive enough to measure
relatively low milliamp values. Maybe you can find an inductive
clamp with these features that connects to your existing multimeter.
Another option is a clamp meter, which is basically a small multimeter with an attached inductive clamp. Electronics Specialties
(www.esitest.com) offers two clamp meters that are better suited
to parasitic drain testing than many previous models. Tool No.
687, which I’ve cited in my Foreign Service column, has a relatively large clamp opening. I’ve used this one on a wide range of
battery cables. The tool features a low-current scale (0 to 4A) as
well as push-button zero capability. Recently, Electronics Specialties released clamp meter No. 688, which has a larger clamp
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PROVEN TECHNIQUES FOR BATTERY DRAIN DIAGNOSIS
To measure voltage drop across a
fuse, slip test lead probes into those
tiny holes in the top of the fuse body.
This gives you access to the terminals
inside the fuse body. This hookup allows your voltmeter to measure voltage drop across a fuse.
This is common example of a parasitic
drain test switch. Turning the green
knob opens and closes the switch. The
multimeter leads are connected
across the switch. Opening the switch
forces battery drain current to flow
through the multimeter.
Thexton’s tool No. 445 neatly closes a
typical door switch located on the vehicle’s B-pillar. Of course, closing this
door switch prevents the interior
lights from turning on and/or a network from waking up while you’re
working on the vehicle.
opening than the previous model, a milliamp scale and the push-button zero feature. I highly recommend the push-button
zero capability on any inductive current
clamp, including those used for parasitic
drain testing.
Understandably, speed and convenience are the key advantages of the inductive current technique. Because you’re
not disconnecting any wiring, you’re not
disturbing the electrical system—a valuable feature when you’re waiting for its
components to go into sleep mode. Some
techs use a clamp meter to complement—
not replace—the test switch. First, they
use it for quick preliminary parasitic drain
readings. For example, with the vehicle in
its “virgin” condition, does the parasitic
drain appear to relatively low or high?
Second, suppose you’ve installed a test
switch on the vehicle and you’re waiting
for components to time out. Meantime,
you’re working on another vehicle. Periodically check parasitic drain on the first
vehicle with the clamp meter. Suppose
you check it several times over the course
of an hour. Let’s say the parasitic drain has
settled down to a consistent, 300mA reading. That strongly suggests that the components have gone to sleep. Third, the
clamp meter has been helpful for those
really tough diagnoses where you want to
check parasitic drain at the customer’s
home or office, for instance.
There is a down side to this approach.
The lower end of the parasitic drain range
is down at the lower end of the typical inductive clamp’s sensitivity.
To use this technique, grab a multimeter with a millivolt (mV) scale, as well as
test leads equipped with pointed probe
tips. After you prep the vehicle for parasitic drain testing, per the directions I
gave earlier, locate the fuse panel. Set the
meter to the millivolt scale and connect its
leads across a fuse. To do this, probe the
tiny holes in the top of the fuse. Connected this way, the meter is measuring the
voltage drop across the fuse.
A meter reading of 0 means no voltage
drop, no current flowing—the circuit is
off. In the case where the circuit powers a
component that normally draws current
when the ignition switch is off, the meter
will show some sort of voltage drop across
the fuse. The greater the voltage drop, the
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September 2014
A Fuse’s Voltage Drop
Measuring voltage drop across each fuse is
the other way to check parasitic drain indirectly. The folks at CARQUEST Technical
Institute (www.ctionline.com) presented
this technique in their training seminars,
and Karl Seyfert discussed it in his December 2010 and January 2011 Trouble
Shooter columns. This method is based on
a simple electrical principle: If no current
flows through a connection, there’s no
voltage drop across the connection. But
when current does flow, there’s a measurable voltage drop across that connection.
Here are just three examples of clamp meter
openings—ESI model
Nos. 687 (top right) and
688 (top left) and
Midtronics No. PDF40.
The ESI models have lowcurrent scales better
suited for measuring
parasitic drain. Even
without a low-current
scale, the PDF40 still
performed pretty well on
low-current measurements. Try out a clamp
meter and satisfy yourself before you buy one!
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vent us from probing them. Furthermore,
these covered fuses often are grouped into
one, much larger fuse assembly. This is a
long row of fuses molded into a single housing. So removing this fuse assembly would
kill several circuits simultaneously—
whether you wanted that result or not.
Network Nuisances
Suppose you encounter two battery cables connected to the same terminal.
When in doubt about where the drain
is, use your inductive clamp to test
both cables at the same time. A larger
inductive clamp such as Midtronics’
PDF40 or UEI’s No. CA30MA (shown
here) may fit around both cables.
greater the parasitic drain. Of course, the
parasitic drain should be within spec or
within the normal range discussed earlier.
Therefore, this approach offers a major
advantage: It pinpoints the exact circuit
that’s causing the excessive parasitic drain
without your installing a test switch or
pulling fuses. The less fuse R&R you do,
the less risk of mistakes such as shutting
off the wrong circuit, accidentally waking
up a “sleeping” computer, etc.
But as I noted earlier, there’s no perfect
test format for diagnosing battery drain.
For example, some fuse panels are in awkward locations. So performing the voltage
drop could put you in a painful, contorted
position—probably on your back. Also,
you can’t perform the voltage drop on
some fuses because there’s no access. You
see, the shell or body of some fuse designs
completely covers the fuse’s terminals. Obviously, you can’t probe covered terminals.
The fuses in late-model Ford products
are an interesting example. Some of the fuses have accessible terminals, others do not.
What’s more, other Ford fuse designs appear technician-friendly because they have
removable, clear covers on them. The trouble is that these transparent covers seem to
break very easily during removal. Worse
yet, the cover’s little retaining tabs on the
main body of the fuse break readily, too.
Many late-model Toyota fuse panels hit
us with a diagnostic double-whammy. First,
some fuses have covered terminals that pre-
Wow, I’ve kept you for a while here.
Hopefully, you’ve gleaned helpful information from this feature. Here are some
closing thoughts on the topic.
Don’t overlook network activity. For instance, suppose you pull the fuse for the
radio and the excessive parasitic drain disappears. Your first instinct may be to
blame the radio itself. But suppose a node
or module on the network is awake when
it should be asleep. That troublesome
node could be talking to the radio; hence,
the drain caused by the active radio is only
the symptom, not the root cause of the excessive drain.
When in doubt, scan the vehicle’s network to see if any modules are awake when
they should be sleeping. The challenge
here is that capabilities vary from one scanner to another. Hopefully, your scanner can
communicate well enough with a network
to confirm which module is sleeping and
which is talking, for example.
Remember, depending on the remote
entry system a vehicle has, someone walking by with a remote fob from an entirely
different vehicle could accidentally wake
it up. Once the system wakes up, your
meter would show an additional, erroneous drain that would disappear when
the entry system goes to sleep again.
When researching a parasitic drain
symptom, watch out for those less obvious
possibilities. For example, if the vehicle
has a natural vacuum evap system, the
ECM could remain awake and energize
the evap system’s vent solenoid valve for
some period of time.
Usually, a professional-grade multimeter
is equipped with a Min/Max capture capability. The Max capture feature may help
you catch the additional parasitic drain a
module creates when it wakes up. Until
next time, good luck and keep smiling.
This article can be found online at
www.motormagazine.com.
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