You go out to your car and the battery is dead overnight, this can be
frustrating to say the least especially when you are late to work or got the
kids ready for school and ready to leave. When the battery looses its
charge in the morning you could have a voltage drain in the electrical system
which is called a parasitic draw. I created this guide which will
show you easy fixes and onward to the more complicated electrical problems. Here are a few
things that can cause this problem which I will go over in more detail in the following guide.
Most common electrical draw problems:
- Seat switch stuck
- Glove box light on
- Trunk light on
- Dome light on
- CD Stuck in player
- ABS relay sticking
- Side mirror switch stuck
- Alternator shorted internally
- BCM or GEM shorted
- Alarm module shorted
- Door lock switch stuck
- Cigarette lighter stuck down
- Vanity mirror stuck on
Scenarios that will be covered:
- My battery is more than three years old
- The car has a sulfur or rotten egg smell and is dead
- I am driving the car with the battery warning light on
- I just installed a new battery and it has lost it's charge
- I smell something burning and now the engine wont crank over
Now that you have an idea of what could be wrong let's go into detail on how
to check for these problems and how to fix them, let's get started.
Your car battery is designed to store electrical power which is used to start
the engine when the key is turned to the crank position. If battery charge
warning light was not on light the last time you drove your vehicle the alternator is
working correctly. If you did notice the warning light on the battery is
probably down on charge which is not the fault of the battery. A sulfur or rotten egg like smell is produced when the battery is shorted
internally either from age or being overcharged by the alternator, in either
case the battery must be replaced and the alternator output voltage checked.
As the battery starts to age, three years or more, it will loose its ability to hold a charge
overnight which is the first sign the battery is ready for replacement.
If you know the battery is good because it has been replaced recently and
it's dead in the morning there is an electrical draw causing this problem. There are several "live" electrical circuits that
bypass the ignition switch that can draw electrical power when
the key is in the off position. Let's start with the most popular and then head
to the more obscure problems.
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 switch with new part which you can get from Amazon or the dealership.
Inspect the glove box light, in most cases this light 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 and its best to check during
the evening time, look for light inside the unit through the small cracks in and
around the box door. If the light is on, open and inspect the light switch to
replace it if needed, or make minor adjustments to help it work correctly and
turn the light off.
Check the cigarette lighters in both front and rear passenger compartments.
Check to see if the lighter itself is stuck down which is usually accompanied by
a fair amount of heat and a burning smell, 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
With the key off while being very quite 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 screw driver.
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 return to its neutral position. If this switch is
broken or stuck it will need to be replaced.
A vanity mirror which is located in the passenger or drivers 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 that is still shining even if the visor is in the up
position. If this is the case pull the visor down to inspect the small pin
switch and repair or replace as needed.
The abs system will stay live when the ignition key is off in most vehicles. This
system has a control relay that is integrated into the module or in the fuse
panel. If when you have the key off and you hear something running under the hood or frame of the
vehicle it's probably this unit. Locate the fuse for the ABS system and remove it
from the fuse panel until
you can replace the module with a new part.
A trunk light may or may not be controlled by the car's BCM depending on the
year and manufacturer of the vehicle. The information I have found on this is
vague to say the least. The good news is it's extremely simply to check if the
truck light is causing the electrical draw problem though it's best to check in
the evening time where observing the light is much easier. 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.
This section is reserved for the more obscure and rare problems, please read
The alternator is used to charge the battery while the engine is running.
When this unit shorts out it can create a draw on the system, to check for this
problem wait until the engine is cold, next 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.
The computer BCM, Alarm and GEM modules 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.
If you 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 15 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.
These next set of problems pertain to older vehicles only, built before 2000
in most cases.
If headlights are left on overnight the battery will be dead, check the
headlight control switch. If the switch is in the on position turn the switch
off, jump start or charge the battery. The battery
should re-gain its state of charge after about 15 minutes of driving.
Once all of the door have been closed check the interior and dome lights,
these lights should turn off after a short amount of time. If the lights stay on
beyond a reasonable amount of time check the interior light bypass switch
located at the headlight switch or on the bezel which also controls the
brightness of the dash lights. You should feel a small bump while rotating the
thumb wheel informing you when the switch is activated or deactivated.
All doors including the lift back or hatch have a pin switch or an internal
switch located in the latch itself that detects when the door is open. When
these switches fail or become misadjusted the interior lights will stay on.
Some SUV's and trucks have an under hood light that is controlled by a mercury
switch which senses the level of the hood. At night look under the
vehicle to check for light near the engine bay, to fix this problem replace the light assembly.
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Article first published 2016-05-21