Parisitic draw

And you have sensors that do not have fuses such as crank sensors, cam sensors, fuel level, coolant level, washer fluid etc etc.
I am sure any sensor circuits that report back to the engine computer are disconnected from drawing on the battery if the ignition is off. Essentially if the computer is not functioning or powered up to manage the engine they cannot draw on the battery.
I should add I have never worked on a CANBUS system so maybe those systems can be activated if the ignition is off. I know body modules can be powered continuously.
 
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I am sure any sensor circuits that report back to the engine computer are disconnected from drawing on the battery if the ignition is off. Essentially if the computer is not functioning or powered up to manage the engine they cannot draw on the battery.
Agreed but the control modules themselves will draw a very small current even with the ignition off. The same for a digital radio.
 
We had a similar problem on a 2018 Subaru outback a couple of years ago, I did all the troubleshooting just like you did and found nothing. We took it to the dealer for diagnosis and they said one of the computers was bad, and it was $1300, but they didn't have one. My wife had done some research online and read where the OEM batteries in those cars were inadequate. Because the battery was over 4 years old, we replaced it with a new one from WM, and the problem went away! But I doubt that is your problem, but if you have another battery to try. On our Farmall C I installed a battery disconnect on the ground cable, that solve the problem with it.
 
Had a fiends Chev. pickup that would kill the battery after about three days idle. Took a little searching, but turned out to be the new stereo they had installed had a circuit that stayed hot, the way they had installed it, moved it to accessory, problem solved.
 
How about something like a lighted mirror on the visor light or a glove box light being on?

If posible, look the car over in total darkness for light from such a thing that's not turning off.
measure the leakage current . There is an initial current spike when the power is initially applied that can pop the fuse in a multimeter .
 
This is on my sons car so I don’t know the make and model but can find out if it makes a difference.

Battery went dead so he charged it up.
Battery is just over 1 year old.
Battery dead the next day so he charged it up but left the battery cables off.
Next day battery is still good so I tell him he must have a parasitic draw.

Today I took a test light over and put between battery negative post and battery cable. Light comes on so yes you have a draw.
We took each fuse out of both fuse boxes one by one but the test light never went off.
Yes we had the doors closed and everything turned off.
I disconnect the alternator as it is not on a fuse but test light never went off.
I am at a loss for what to try next.

A "parasitic drain tester" is a great tool for diagnosing such problems.

You connect it up with the test switch closed, (which gives full battery voltage to the computers and other systems) then after allowing time for the systems to "go to sleep" you open the test switch and read the remaining battery drain current. Only thing I don't agree with in the video is only allowing 10 seconds for the modules to shut down before opening the test switch.
 
This would be dependent on the capabilities of the ammeter. If it is only capable of carrying 10 amps of current you would want to place a 10 amp fuse in series between the cable and post to see if it pops the fuse to protect your meter before proceeding with connections to it. What I have also seen is a higher draw for a few seconds and then drops way down as if a capacitor has been charged. The ammeter method should eliminate this interference with your test. Also you need to disconnect the alternator wires, the main terminal definitely will not be fused. Well I should say at least they were not back in the day 1990s. Which brings up another point most new cars have a panel of heavier fuses under the hood. Those would also need pulled. Also since you said you did them one at a time that is not a complete test. You need to end up with no fuses left in the panel. Take a picture with your phone to speed up reinstallation. The ammeter would lower the possibility of this but for example, if one circuit had a low draw that the battery tolerated for say a week it still may be enough to light your test light. But at the same time another circuit developed an issue that has a higher draw that causes the battery to drain in one day. If you pull the fuse for the circuit that is the one day draw the one week draw circuit has the fuse you put back in you will never find the problem. In the end a total and complete test is reinstalling the fuses each by themselves only to complete each circuit individually. Also this should have been at the beginning, if your test light is a LED unit you will likely never determine which circuit had the draw, it only take milliamperes to light one of those. You need a test light with an incandescent bulb for this kind of testing.
Every quality meter I have ever used has an internal amp fuse on the current leads. From a Simpson 260 to my Fluke that I’m using now.
 
Remove negative cable from battery, put red lead on negative cable and black on negative battery post.

Set meter move selector to 5A, move red lead to 5ADC. when done don't forget to move red lead from 5ADC are you will blow the meter fuse on your next voltage test. Go to the 20:00 mark on the link "How its done" you don't need the extra cables he uses.

voltmeter.jpeg
 
John
It looks like HoBo posted this before I finished typing.
Move the red test lead up one position to the 5 amp. Then move the selector switch to the 5a position. Then use the meter like you did the test light. Typically most vehicles use about .050 amps, 50 ma. If 50 ma drains the battery overnight, you have a problem with the battery. Take it to any auto parts store and have them test the battery.
Finding parasitic loads is not easy. Most vehicles will draw a few amps until the interior lights turn off.
Report back how many amps your meter reads. You can't hurt the meter on the 5 amp range unless you try measuring 120 vac on the 5 amp range. Then you will melt the meter leads.
My Kubota owners manual says the battery will discharge 1 percent in 2 days.
My 2007 GMC battery will lose about 1 percent of its charge in a day. My truck is parked in the garage and rarely do I drive it. If I disconnect the battery it doesn't self discharge as much. So when it's parked, I put a charger on it. I'm not sure how old the battery is. As long as the charger keeps the battery up all is good. My drain is 50 ma. So my battery is past it's best use by date. No guarantee a one year old battery isn't past it's best use by date.
In the future I think I may only use an AGM battery in car, truck, and Kubota.
AGM battery costs more, but lasts longer. No need to clean battery terminals.
I ordered my last AGM from
IMG_20241228_122712.jpg
summit racing, Saved $100 over any auto parts store in TH.
 
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Thinking back over this info, a parasitic drain is not
going to drain a battery in a day. Got to be more of
a drain than that. Even a trunk light shouldn't drain
a good battery in a day.
Jim
 
Thinking back over this info, a parasitic drain is not
going to drain a battery in a day. Got to be more of
a drain than that. Even a trunk light shouldn't drain
a good battery in a day.
Jim
"a good battery" So how can you confirm a good battery the question is always how to confirm a bad battery. This is where these type of questions get lost in a post. The only gold standard I know of is use a carbon pile load tester are play with a hydrometer that still leaves a question of is it good. . No other way than a carbon pile load tester I know of will positively confirm a battery is good. You may be proud of your TOY tester but its not a confirmed test. When I make the statement can it with out a doubt confirm the battery is good folks with those toy testers run off and hide.

There are other ways to perform a good Parasitic drain test but its hard to beat a voltmeter using the amp setting. Day in day out its a true test without a doubt. All those doodads and extra cables add safety to the process and help protect your Equitment but they are not needed. You are going to make mistakes its part of the gig. Talking about mistakes with out a doubt 5A is not enoufh 10A would save some fuses : )
 
Thanks guys
I will have to get back to this later.
My son (against my advise) took the car; a set of jumper cables; and the starting battery out of my boat as a backup; to Florida for a visit with inlaws. Said he would take the battery cable off each night till he got back and we could do some more testing.
 
I am sure any sensor circuits that report back to the engine computer are disconnected from drawing on the battery if the ignition is off. Essentially if the computer is not functioning or powered up to manage the engine they cannot draw on the battery.
I should add I have never worked on a CANBUS system so maybe those systems can be activated if the ignition is off. I know body modules can be powered continuously.
I was schooled a little differently concerning bad sensors and patristic drain.. And like I said before. Some newer cars needs testing that can take upwards from 24 to 48 hours to test.

https://poweringautos.com/can-a-bad-sensor-drain-a-car-battery
 
I was schooled a little differently concerning bad sensors and patristic drain.. And like I said before. Some newer cars needs testing that can take upwards from 24 to 48 hours to test.

https://poweringautos.com/can-a-bad-sensor-drain-a-car-battery
Sure hope no $ were spent on generating this article! Sure it gave info on what sensors do/supposed to do and results of malfunction, but virtually zero on how to isolate the unwanted drain, which was supposedly the whole point!
 
Sure hope no $ were spent on generating this article! Sure it gave info on what sensors do/supposed to do and results of malfunction, but virtually zero on how to isolate the unwanted drain, which was supposedly the whole point!
That does not make a lot of sense.
Like a doctor putting a cast on your leg when you have a kidney stone.
Without the proper testing with the correct tools to conduct such testing. How can you isolate a problem?
A $2.00 multimeter is not going to tell you that your car has a bad sensor that causes the computer to still have power when the key is off.
 
John
It looks like HoBo posted this before I finished typing.
Move the red test lead up one position to the 5 amp. Then move the selector switch to the 5a position. Then use the meter like you did the test light. Typically most vehicles use about .050 amps, 50 ma. If 50 ma drains the battery overnight, you have a problem with the battery. Take it to any auto parts store and have them test the battery.
Finding parasitic loads is not easy. Most vehicles will draw a few amps until the interior lights turn off.
Report back how many amps your meter reads. You can't hurt the meter on the 5 amp range unless you try measuring 120 vac on the 5 amp range. Then you will melt the meter leads.
My Kubota owners manual says the battery will discharge 1 percent in 2 days.
My 2007 GMC battery will lose about 1 percent of its charge in a day. My truck is parked in the garage and rarely do I drive it. If I disconnect the battery it doesn't self discharge as much. So when it's parked, I put a charger on it. I'm not sure how old the battery is. As long as the charger keeps the battery up all is good. My drain is 50 ma. So my battery is past it's best use by date. No guarantee a one year old battery isn't past it's best use by date.
In the future I think I may only use an AGM battery in car, truck, and Kubota.
AGM battery costs more, but lasts longer. No need to clean battery terminals.
I ordered my last AGM fromView attachment 98813 summit racing, Saved $100 over any auto parts store in TH.
Showing a battery charger, or volt meter attached that way is fine if the caption and intention is to measure voltage, or show charging attachments. the thread is neither and may result in damage to meters or smoke/blown fuses! Jim
 
Thanks guys
I will have to get back to this later.
My son (against my advise) took the car; a set of jumper cables; and the starting battery out of my boat as a backup; to Florida for a visit with inlaws. Said he would take the battery cable off each night till he got back and we could do some more testing.
Easiest way to test a battery is replace it with a battery from another vehicle. If it goes dead over night it's not the battery. Used to be batteries were dry until you bought them then the salesman would put the acid in them and charge them. Now they take one off a shelf and say there you go. Maybe been sitting there for years. As for parasite drain one time it was the vanity light staying on on the visor and one time it was the window motor switch on rear windows on my car.
 
This is on my sons car so I don’t know the make and model but can find out if it makes a difference.

Battery went dead so he charged it up.
Battery is just over 1 year old.
Battery dead the next day so he charged it up but left the battery cables off.
Next day battery is still good so I tell him he must have a parasitic draw.

Today I took a test light over and put between battery negative post and battery cable. Light comes on so yes you have a draw.
We took each fuse out of both fuse boxes one by one but the test light never went off.
Yes we had the doors closed and everything turned off.
I disconnect the alternator as it is not on a fuse but test light never went off.
I am at a loss for what to try next.
I had a similar problem in my Explorer. It turned out to be my daughter's Apple Lightning phone charger shorting out to a metal part in the cab. I suggest making sure there are no phone charger cables hiding in the car. Easy check. Common problem.

Cliff(VA) now (NC)
 

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