We are a team of ASE certified mechanics who have created this battery draw or dead overnight guide to help you save money by walking you through what to look for first. A drain in the electrical system is called a parasitic draw.
An electrical system can be complex with many relays, computers and switches. When one of these items malfunctions it can cause an electrical draw which creates a battery drain. If the battery warning light has come on prior to the problem then the battery should be okay and the alternator has failed.
Electrical draws can be tricky because the problem can be found in five minutes or four hours depending on the severity of the issue and the honesty of the repair shop.
We'll go over the easy stuff and then escalate to the more difficult issues.
The most common problem for a battery to be dead in the morning or after the
car has been sitting for a time is a weak battery. To confirm this issue
charge the battery, then
use this battery load test guide which
is easy because there is no tools or equipment needed. If the
battery fails the load test it will need
to be replaced. A sure sign the battery is bad is a sulfur or rotten egg like
smell. A battery will typically last between 3 to 4 years in most cases, if the
battery is okay please continue.
The ignition switch will cut the power to many of the vehicle's electrical circuits.
There are several "live" electrical circuits that bypass the ignition switch which
draw electrical power when the key is off which is what we will concentrate on,
these checks are quick and easy to do. Inspect the glove box light which is controlled
by a small pin switch inside the box door frame. If this switch malfunctions or
is misaligned it will allow the light to stay on draining the battery. This can
be sometimes tough to see in the bright light of day so it's best to check this
during the evening time. Look for light inside the glove box through the small cracks
in and around the box door. If the light is on, open and inspect the light switch
to replace if needed, or make minor adjustments to help it work correctly and turn
the light off. This can be applied to the trunk light as well. Pop the trunk open
to observe the light, then slowly close the lid while watching the light through
a small opening near the rear of the trunk lid, the light should go off. If the
light stays on, replace or adjust the pin control switch or trunk latch.
Check the cigarette lighters in both front and rear passenger compartments to
see if the lighter itself is stuck down which is usually accompanied by a fair amount
of heat, pull the lighter upward to stop the electrical draw, in this case the lighter
has gone bad and needs replacement.
When you shut the ignition key off the radio turns off as well, this is not true
for the CD player and changer. If a CD gets stuck in the load or eject position
it will continue to work the small motor inside the player while draining the electrical
system. With the key off listen closely to the player, if you hear a motor running
a CD is stuck. Try to work the CD either in or out using a small tweezers or flat
blade screwdriver. If you cannot retrieve the CD, pull out the radio fuse until
you can replace the unit or have it repaired, this will stop the battery draw.
The door lock switch is constantly hot or live with electrical power. Sometimes
the control switch will get gummed up with dirt or soda which makes the switch stick
in the lock or unlock position. This will force the lock actuator in the door to
stay on which will draw the battery down. Inspect the lock switch to make sure it
returns to its neutral position. If this switch is broken or permanently stuck,
replacement is required.
The side view mirror switch continues to get power after the ignition switch
is off. This switch like other switches can get gummed up from grime and soda which
can hold the switch on forcing the motor to draw power. Check the switch operation
to ensure that it returns to its neutral position. If this switch is broken or stuck
it will need to be replaced.
Inspect the electric seat control switches, this switch can become sticky or
weak allowing the switch to stay engaged forcing the seat motor to draw power from
the battery. To check for this condition observe the operation of the seat control
switch if it doesn't return to it's neutral position or is sticking in one position
replace the seat switch
with a new part which you can get from Amazon or the dealership.
A vanity mirror located in the passenger or driver's side sun visor has a light in most cases that can stick on. To check for this problem move the visor slightly downward to observe a light, if the light is still on in the up position pull the visor down to inspect the small pin switch and repair or replace as needed.
We feature additional problems below
When a component is left on for extended periods of time it will heat up. This can be due to a bad sensor, sticking relay or a failed computer, also a low hum such as a fuel pump or ticking such as a HVAC blend door actuator can be a clue as well. Start in a quiet place with the vehicle cold and the battery fully charged.
A control relay is a small electrical component that turns on and off larger
items such as a fuel pump or an air conditioning compressor. When a
relay goes bad they can "stick" causing the component to stay on even when the
key is off. Locate the under hood and interior fuse and relay panels and remove
their covers. Next, touch each relay to check for heat, if a relay is found remove
and replace it with a new relay.
Check for warm components such as the alternator, air conditioner compressor
clutch and electric steering rack motor (if equipped). Locate the alternator and
feel it with your hand to check for warmth, if the alternator is warm with a possible
burning smell there is an internal short and the
alternator must be replaced.
Listen to the vehicle by sitting inside, lift the hood and trunk and try to hear
anything that might be left on indicated by a hum or light ticking. In this case
the ABS control module was
stuck on creating a low hum and needed to be replaced.
The Powertrain Control Module (PCM) Body Control Module (BCM) or Security Module can internally short circuit which can cause various electrical systems in the car to stay "live" which creates an electrical draw. This problem can be checked by locating the fuse of the systems and removing them or removing the controllers altogether. If the vehicle starts the next morning you have found the problem. Also a CAN scan (controller area network) will sometimes detect a malfunctioning computer.
If you have completed this guide and still can't find the cause of the battery drain, a manual draw check of the electrical system will need to be performed. With the ignition key in the off position and the doors closed (driver's side window down) wait 15 minutes, then disconnect the battery cable on the negative side, (Note: A fifteen minute wait time allows the computers to go into "sleep mode" which shuts down most electrical systems). Attach a test light between the negative battery cable end, and the negative battery terminal, the test light should light up dimly or not at all. If the test light is on brightly there is a strong electrical draw in the system. To locate the draw start removing fuses one at a time, when the test light goes out the circuit in question has been located. Identify all accessories in a particular circuit by using a wiring schematic.
An alternative method is to use a voltmeter to perform a manual draw test. With the ignition key in the off position and the doors closed (driver's side window down) disconnect the battery cable on the negative side. Set your voltmeter on the DC amp scale, then attach the red lead to the negative battery post. Attach the black lead to the battery negative cable. Use a small jumper wire along side of the voltmeter and wait for 15 minutes to allow the modules to go to sleep. Then remove the small jumper wire leaving just the voltmeter. Then look at your reading, it should be about 50 to 75 milliamps which is considered a normal draw to keep the modules backup systems charged. If the draw is higher than that, then start removing the fuses one by one until the draw drops to the normal levels. Once you find the fuse, you will need to look for a power distribution wiring diagram that will show what components are fused on that circuit. Install the fuse and go to each component on that circuit and disconnect them one at a time until the draw drops to the normal range. At this point, you have found the draw. Replace the component and recheck the draw to confirm your repair.
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