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Old 12-31-2021, 04:48 PM   #1
EasyGoing1
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Default Neighbor has a constant drain on his car battery...

So my neighbor has been asking me for jump starts like every other day ... and said he didn't know why his battery kept dying, so this morning, I grabbed my Fluke and went over and said, let's go figure this out ... ultimately, his alternator was kicking out a nice solid 14.8 volts even under heavy load, so we let the battery charge for a while, then after he turned the car off, I put the amp meter on it and saw that the battery was kicking out a constant 300ma with everything turned off, doors closed, key out of the ignition, etc...

So I figured the best course of action would be to start pulling fuses to find out which circuit was draining the battery and it ended up being a fuse labeled as "BACK UP" - whatever the hell that meant, but googling the year make and model with that fuse name turned out some old (10 years in some cases) forum discussions on this exact issue with that exact car ... but none of them ever got to a resolution as to what the problem is or how to fix it.

The fuse powers the head unit ... but this car has an aftermarket unit which I know doesn't matter, but that would at least tell me that the issue is not necessarily with the stereo itself since the blog posts all had stock stereos except for one, and he ended up swapping back in his stock head unit which did NOT fix the problem.

I told him that for now, just pull the fuse when he parks the car until I can figure out how to actually solve the problem.

The vehicle is a 2002 Acura RSX ... if anyone has any words of wisdom, I'm all ears.

Thank you,
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Old 12-31-2021, 06:25 PM   #2
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Default Re: Neighbor has a constant drain on his car battery...

looks like you have fixed it .
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Old 12-31-2021, 06:33 PM   #3
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Default Re: Neighbor has a constant drain on his car battery...

does it have a power antenna that's jammed?

Then the other possibilities are like keyless entry, security system, etc., etc... did that fuse disable other things along with the battery drain?

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Old 12-31-2021, 06:53 PM   #4
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Default Re: Neighbor has a constant drain on his car battery...

unplug the stereo then see because its not stock .
looks like honda use that fuse for a few things . but rule out easy first .

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Old 12-31-2021, 06:54 PM   #5
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Default Re: Neighbor has a constant drain on his car battery...

read the current and then unplug the head unit - see if it still draw's
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Old 12-31-2021, 09:13 PM   #6
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Default Re: Neighbor has a constant drain on his car battery...

The limit is about 125mA for automotive parasite draw.

Although you see 300mA, give it 5 minutes or so. After key-off an ECU does some house-keeping before it goes to sleep. So it might be stuck (software) waiting for something and never seeing it, so it stays running. You'd need to check for OBD trouble-codes.
My NAV takes its leisurely time shutting down after key-off, the OS does a bunch of crap then it powers down a minute or two after.
I've got some relay that goes CLUNK about 5 minutes after I turn the engine off, so something is running for that time.

While the car is parked, the BCM is always on to receive remote key fob signals. If the engine is hot the fuel pump will periodically cycle to pump cool gasoline preventing fuel percolation in the fuel rail. ECU will do a canister leakdown test etc. So there are things going on despite the key being off, which are normal. A parked car can make some odd noises.

Subaru have a huge problem with high parasite draw and ECU firmware update helped a little but they are notorious battery killers. People just use a charge maintainer, not much else you can do as they have a poor design.

Hardware-wise, an alternator voltage regulator can cause parasite drain but it's usually high 3-4A for the field winding and more for a shorted rectifier.

My friend's old '69 Ford Custom 390 had the Holley electric choke (heater) wired to the battery drawing 2A all the time, for years. He'd given up and stuck a massive disconnect switch on the battery lol.
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Old 12-31-2021, 10:24 PM   #7
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Default Re: Neighbor has a constant drain on his car battery...

Ideally one doesn't consume too much of a battery over 2 weeks, say cannot drain a battery more than 75% over that period so you can still power 4 horsepower to start the car...
So at 50Ah typical battery, ¾ of full capacity and 2 weeks, it comes out just about 100mA constant key off drain...

If you're draining the battery every 2 days at 300mA, the battery is probably weak and should be replaced, but 300mA is quite bad.

Kind of funny: I noticed someone carrying a Li-ion jump starter pack with him as if he knew he needed to jump start his car frequently. In reality he needed to just buy a new battery for his car...
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Old 01-02-2022, 09:30 AM   #8
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Default Re: Neighbor has a constant drain on his car battery...

Quote:
Originally Posted by eccerr0r View Post
Ideally one doesn't consume too much of a battery over 2 weeks, say cannot drain a battery more than 75% over that period so you can still power 4 horsepower to start the car...
So at 50Ah typical battery, ¾ of full capacity and 2 weeks, it comes out just about 100mA constant key off drain...

If you're draining the battery every 2 days at 300mA, the battery is probably weak and should be replaced, but 300mA is quite bad.

Kind of funny: I noticed someone carrying a Li-ion jump starter pack with him as if he knew he needed to jump-start his car frequently. In reality he needed to just buy a new battery for his car...
He said the battery is less than a year old, and it when it started doing this, he was needing a jump like every several days, then it got down to almost every day where he had a routine going so that if he went out and started his car at about 10:00 at night and let it run for a half an hour, he could shut it off and be able to start it in the morning and get to work ... but if he did that at 7:00 pm ... then it wouldn't start in the morning ... 300 to 400 ma is a lot even for a car battery and his isn't all that big of a battery in the first place. I'd say it's one of the smaller ones that I've seen.


Quote:
Originally Posted by eccerr0r View Post
does it have a power antenna that's jammed?
Then the other possibilities are like keyless entry, security system, etc., etc... did that fuse disable other things along with the battery drain?
I found a 1300 page shop manual for his car online and looked at the schematics where that fuse is concerned and it connects to a whole slew of systems in the car, including gauge functions, radio, and even door lock switches. It is labeled as a BACKUP so maybe it's some kind of redundant fuse though I don't recall seeing any in parallel ... though there might have been ... that car is FAR more complex than I ever thought it would be - being 20 years old. And the shop manual has all kinds of self-tests you can initiate by doing all these different dances with the key and buttons and timing the actuation of each in different patterns ... what a nightmare.



Quote:
Originally Posted by redwire View Post
The limit is about 125mA for automotive parasite draw.

Although you see 300mA, give it 5 minutes or so. After key-off an ECU does some house-keeping before it goes to sleep. So it might be stuck (software) waiting for something and never seeing it, so it stays running. You'd need to check for OBD trouble-codes.
...
My friend's old '69 Ford Custom 390 had the Holley electric choke (heater) wired to the battery drawing 2A all the time, for years. He'd given up and stuck a massive disconnect switch on the battery lol.
That's pretty funny ...

We actually had the meter on it for the better part of two hours while we looked around for the fuse box and then we troubleshoot his rear hatch which wasn't unlocking - turned out a screw came loose and it wasn't getting any leverage to slide the latch open so we fixed that ... then we sat around and bullshitted for a while ... and over that course of two hours, the battery was still draining that same amperage, though Im still not ruling out the ECU staying engaged because of some other problem, that might be in the car making the ECU THINK that things are not settled down enough for it to go into sleep mode. Not sure how to test that though ... I wonder if I could talk to it over ... what's it called ... CAN-BUS or something like that? I know people do that with Arduino's all the time.
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Old 01-02-2022, 10:00 AM   #9
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Default Re: Neighbor has a constant drain on his car battery...

I know this not going to be easy however if you were to unplug the seat controller window controller and interior lights and things that might be stay on one thing that might be going on is that the automatic sensor that controls the headlights if has this feature not turning off completely

And as a last resort unplug the computer for the car and see if goes away one other thing that might be an issue is some cars have leveling feature that might not be working correctly anymore hood light or trunk light staying on

From some of wiring diagrams I saw there are at three amp for the radio and one of could not be shutting down correctly

On rare occasions I have even seen alternator voltage regulator go bad and keep the field winding on so I would not rule this out either but this easily found after a couple of the engine not running just feel the back of the alternator it should have the same temperature as the outside temperature is

I have even seen the starter switching get stuck where it keeps some of electrical system on some what activated which should not happen but I have seen this before as well

In a former life I was a certified auto electrical technician I saw all kinds of issues that sometimes were not easily resolved

My son has a very new car and for some reason the computer did not shut down completely and he found his battery almost completely dead come to find out that he had left the car door not completely closed and looked so the computer display center did not shut down completely

I ran the test that you waited to see if the computer shuts down and goes to sleep mode or not one note it was very hard to reset the computer so it would shut down completely and go to sleep after he had left the door that way

I hope this helps you
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Old 01-02-2022, 02:32 PM   #10
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Default Re: Neighbor has a constant drain on his car battery...

Take that battery out, clean the terminals on the car and clean the whole battery and it’s terminals. Charge the battery on a charger until it’s full and put it back in. By that time all the little computers had plenty time to “reset”. Put the current clamp on the battery, open up the drivers window (just in case) close all the doors and wait 30 mins in order for the modules to go into sleep.
Depending on the car, some board computers know that the hood is open (plus the light on the hood goes on) you have to find that switch, other than that not all modules go into sleep mode.
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Old 01-03-2022, 12:03 AM   #11
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Default Re: Neighbor has a constant drain on his car battery...

Quote:
Originally Posted by EasyGoing1 View Post
though Im still not ruling out the ECU staying engaged because of some other problem, that might be in the car making the ECU THINK that things are not settled down enough for it to go into sleep mode.
If you are worry about ECU doesn't go to sleep mode you can check the voltage pinout from socket that goes to ECU, with proper multimeter.



I have same problems with my dad's car. it turns out the relay is stuck, melted down inside and many cable stripped by rats causing parasitic leakage.
condition: around 2 Amps drawn, with bad 100Ah (real test around 40-60Ah) , so it should be 20-30 hrs completely dead but it didn't crank if left behind 10 hours. (as it should be because you need huge current to crank it)

but as suggested by others 300mA isn't bad at all even on 24hours

with 45Ah battery GEL or AGM and 300mA draw is around 130 Hours to completely dead (9.6V-10.6V and take it half time around 65 hours the car won't crank at all)

unless your neighbor have less capacity or weak battery. around 10Ah (30 hours to completely dead) so give it or take 15 hours the car won't crank at all.

I hope you find the culprit quick enough. and go tell him to change the battery with bigger capacity.

New battery isn't always good, some bad shops put recycled battery with new box, i have experienced some bad new battery, it usually 2 Years to change the battery but this time less than 6 months.
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Old 01-03-2022, 04:24 AM   #12
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Default Re: Neighbor has a constant drain on his car battery...

Better way to check parastic drain is measure voltage drop on fuses. When you pulled fuses, the CAN network can wake up and raise the voltage.
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Old 01-03-2022, 11:50 PM   #13
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Default Re: Neighbor has a constant drain on his car battery...

Quote:
Originally Posted by faraday28 View Post
If you are worry about ECU doesn't go to sleep mode you can check the voltage pinout from socket that goes to ECU, with proper multimeter.

...

but as suggested by others 300mA isn't bad at all even on 24hours

with 45Ah battery GEL or AGM and 300mA draw is around 130 Hours to completely dead (9.6V-10.6V and take it half time around 65 hours the car won't crank at all)

unless your neighbor have less capacity or weak battery. around 10Ah (30 hours to completely dead) so give it or take 15 hours the car won't crank at all.

I hope you find the culprit quick enough. and go tell him to change the battery with bigger capacity.

New battery isn't always good, some bad shops put recycled battery with new box, i have experienced some bad new battery, it usually 2 Years to change the battery but this time less than 6 months.
I completely agree with the math and the theory behind the expected charge hold times of the battery ... but so far, all of the automotive forums I've been reading suggest that on a "normal" car battery, parasitic drain should not ever be above 10ma with anything over 100 being too much ... now in this situation. it very well could be that this 300ma drain took a long time to completely drain the battery. And given that he only lives 10 minutes away from his work, those short drives might not have been enough time to recharge the battery to a capacity where 300ma would survive the night. At least that's my assumption on this issue.
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Old 01-04-2022, 12:17 AM   #14
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Default Re: Neighbor has a constant drain on his car battery...

Quote:
Originally Posted by CapLeaker View Post
Take that battery out, clean the terminals on the car and clean the whole battery and it’s terminals. Charge the battery on a charger until it’s full and put it back in. By that time all the little computers had plenty time to “reset”. Put the current clamp on the battery, open up the drivers window (just in case) close all the doors and wait 30 mins in order for the modules to go into sleep.
Depending on the car, some board computers know that the hood is open (plus the light on the hood goes on) you have to find that switch, other than that not all modules go into sleep mode.
I did check those terminals and they are totally spotless ... which makes sense since he told me that the battery was replaced less than a year ago.

Since I can plainly see that the current drain goes away by removing that fuse, I know which circuit is causing the problem, I just don't know which YET which system on that circuit is responsible.

Taking the battery out and doing a full charge on it is a good idea and I will definitely do that the next time we start troubleshooting again which will most likely be this coming Saturday.
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Old 01-04-2022, 12:36 AM   #15
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Default Re: Neighbor has a constant drain on his car battery...

Quote:
Originally Posted by sam_sam_sam View Post
I know this not going to be easy however if you were to unplug the seat controller window controller and interior lights and things that might be stay on one thing that might be going on is that the automatic sensor that controls the headlights if has this feature not turning off completely

And as a last resort unplug the computer for the car and see if goes away one other thing that might be an issue is some cars have leveling feature that might not be working correctly anymore hood light or trunk light staying on

From some of wiring diagrams I saw there are at three amp for the radio and one of could not be shutting down correctly

On rare occasions I have even seen alternator voltage regulator go bad and keep the field winding on so I would not rule this out either but this easily found after a couple of the engine not running just feel the back of the alternator it should have the same temperature as the outside temperature is

I have even seen the starter switching get stuck where it keeps some of electrical system on some what activated which should not happen but I have seen this before as well

In a former life I was a certified auto electrical technician I saw all kinds of issues that sometimes were not easily resolved

My son has a very new car and for some reason the computer did not shut down completely and he found his battery almost completely dead come to find out that he had left the car door not completely closed and looked so the computer display center did not shut down completely

I ran the test that you waited to see if the computer shuts down and goes to sleep mode or not one note it was very hard to reset the computer so it would shut down completely and go to sleep after he had left the door that way

I hope this helps you
Here is the shop manual for this car ... the fuse in question is in the fuse box that is in the engine compartment, and it is tagged in the shop manual as "UNDER-HOOD FUSE/RELAY BOX" Fuse No. 9 (7.5 A)

You can see that there are several systems connected to that fuse, and a couple of them have a self-diagnostic mode that can be enabled with a dance as the book describes.

Also, I did check the alternator and it's kicking out 14.8V consistently, even under load so I'm thinking the voltage regulator is doing it's job nicely.

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Old 01-04-2022, 07:35 PM   #16
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Default Re: Neighbor has a constant drain on his car battery...

Quote:
Originally Posted by EasyGoing1 View Post
I did check those terminals and they are totally spotless ... which makes sense since he told me that the battery was replaced less than a year ago.

Since I can plainly see that the current drain goes away by removing that fuse, I know which circuit is causing the problem, I just don't know which YET which system on that circuit is responsible.

Taking the battery out and doing a full charge on it is a good idea and I will definitely do that the next time we start troubleshooting again which will most likely be this coming Saturday.
An almost dead battery (car barely starting) can also cause all kinds of “idiot lights” to come on. Happened to me before. If it is an aftermarket stereo that’s the problem, check if it is wired correctly. Radio turns off when the key is out etc.
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Old 01-04-2022, 07:46 PM   #17
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Default Re: Neighbor has a constant drain on his car battery...

first thing is be sure the key is far enough from the car when its parked as some cars it can keep things awake . next thing is check for call backs to update firmware/software .
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Old 01-05-2022, 05:14 AM   #18
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Default Re: Neighbor has a constant drain on his car battery...

My neighbor's son has a 2004 Acura TL with the 3.5-litre engine. Automatic gearbox. For a short time, a year or two ago, his battery drained several times over the time span of a few weeks. Some internet posts suggested there was a capacitor problem in the bluetooth module (just inside the dashboard near the driver's left knee). Perhaps the car was trying to link up with his bluetooth cell phone all night long while he was in his bed sleeping.

As far as I know, the problem went away on its own. I'm sorry we never got to track down this issue.

It sounds like you are on the right track and will shortly fix the problem. Good luck to you !
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Old 01-10-2022, 09:36 AM   #19
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Default Re: Neighbor has a constant drain on his car battery...

Quote:
Originally Posted by EasyGoing1 View Post
Here is the shop manual for this car ... the fuse in question is in the fuse box that is in the engine compartment, and it is tagged in the shop manual as "UNDER-HOOD FUSE/RELAY BOX" Fuse No. 9 (7.5 A)

You can see that there are several systems connected to that fuse, and a couple of them have a self-diagnostic mode that can be enabled with a dance as the book describes.

Also, I did check the alternator and it's kicking out 14.8V consistently, even under load so I'm thinking the voltage regulator is doing it's job nicely.
Here is something else. Just because the alternator "appears" to be charging at the correct voltage, does not necessarily mean the alternator is good. There are 4 huge diodes inside the alt. They can and do leak voltage. If one is leaking, it will drain the battery. The ripple of the alternator needs to be checked. A bad or leaking diode will show up in a ripple test. If you remove the large positive post and unplug the connector to to alternator and the draw goes away, you have found your problem. Either a leaking diode, or a bad regulator.
I have not studied this vehicle yet, but on most modern vehicles, the regulator is actually located either in the ECM (Engine Control Module) or in the BCM (Body Control Module). I have seen a DLM (Door Lock Module) drain a battery. Some of these DLM's have the receiver for the RKE (Remote Keyless Entry) system in them. Most vehicles have the RKE receiver located in the instrument cluster and have remote antennas or the RKE module serves as the "antenna".
These draws on these newer vehicle will make you pull your hair out! Trust me! I spent two weeks looking for a 350ma draw on a police vehicle and it ended up being in the TCM (Transmission Control Module).
Don't even bother trying to pull codes on that vehicle without a dealer level scan tool. All you will get are the federal mandated "OBDII" codes. Manufacturers are not required to (and they absolutely do not) make available vehicle specific codes and/or live data for every system in the vehicle.
Acura is Toyota, and they have notoriously difficult computer systems in them. There are HUNDREDS of possible codes! A consumer level scan tool will only give you access to maybe %10 of these at the most.
My experience tells me you are either dealing with a leaking alternator, or something to do with the vehicles security/immobilizer system. Repairing the security/immobilizer will require a dealer level scan tool. The days of repairing your vehicle yourself (unless your a professional mechanic) are pretty much gone! Good luck and I'll watch this thread and see if I can help you more. I have access to all of Acura/Toyota's TSB's (Technical Service Bulletins). If you will give me the year/make/model and the last 8 of the VIN, it would help me immensely.
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Old 01-10-2022, 12:24 PM   #20
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Default Re: Neighbor has a constant drain on his car battery...

Acura is Honda, Lexus is Toyota.

Acura/Honda 4-cyl do use the smallest car battery group 51R which really belongs in lawn tractors lol. It's at best 35-40Ahr.
I'm a bit suspicious the system voltage can hop up to 14.8V like that, it implies the battery resistance is high or is low in water, or the alternator is maxxed out.

With the 350mA drain, that is in the range of small solenoids. A shorted mosfet in a body or transmission control module would leave a solenoid on all the time.
Is there anything else on the car malfunctioning?
All you can do is unplug loads until it stops, to narrow it down.
Most solenoids and motors are higher current - door locks, power windows have a PTC for lower holding current if stuck on.

Chrysler/Jeep has nutty cabin vent and duct motors that open/close everytime you start/stop the vehicle, to wear them out faster. You can hear them close/home after being parked for 5 minutes. Very hard to fix say intermittent heat or recirc with the hyper computer-controlled duct motors. Their current is low a few hundred mA but again they run off the battery.
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