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Something is draining my battery when the car is turned off

nsxotic911

nsxotic911

Legendary Member
Joined
6 November 2006
Messages
3,360
Location
Austin, TX
If I don't keep my car on a battery tender, I can't have the car off for more than a week without the battery getting *completely* dead. It has been like this since I bought the car years ago.. I always thought that it's because I just didn't drive it and forgot to put it on a battery tender when I wasn't driving it (months at a time :( ) but testing it out over the last couple of weeks - when i drove the car for about a week and then didn't drive it for a week, the car might as well not had a battery, that's how dead it was..

I have a Optima 1200 that is < 1 year old as I had already 'burned' through my 925 prior.

How is this possible? How do I track it down? I've removed my headunit so that can't be it. I had an aftermarket car alarm system that I "removed" - I'm wondering if I missed something along the way. I removed the horn, the ignition harness, electronics etc..

Ideas??
 
Get the battery tested as well. As 8400RPM mentioned it may just be defective and incapable of holding a charge.
 
Also, clean up any corrosion/crystals around the battery terminals (baking soda and water does the job). Last time I got my NSX washed, the battery went completely flat (no click, no lights) a day later. Turns out some splash from the wash wet the crystals and there was a short between the posts...

After cleaning and charging, all is well.
 
I had this issue a few yrs ago with constant draining, battery after battery, maintenance checks IE: Alt, Terminal posts, connections etc... Nothing. Same thing happened to my vette. I could not find any related source with the NSX so I checked the vette forums. The vette was easier since the trunk area can be seen through the drivers area. I took my phone turned on a flash light and recorded the trunk insides with my phone as I closed it. Culprit.. Light was staying on with the lid closed. Adjusted the trunk to close tighter and have not had any issue since. Your may not result the same but does not hurt to check.
 
If it comes to it, place an ammeter in series with one of the battery terminals and look for a current flow when everything is off. I am not sure but there is likely to be some very slight flow from the need to keep some of the electronics live under normal conditions. You are looking for something significant.
Pull the fuses one at a time. That should help identify the circuit that is killing the battery. After that...the work begins: sorting out exactly what is happening, but at least you will have a diagnosed circuit to troubleshoot.
Good luck and keep us posted.
 
I'm having exactly the same problem. We did the ammeter test and it says it's pulling 120ma, which I think is 2 or 3 times normal?

Looks like the fuse that runs the "interior lighting" circuit is the culprit, but we haven't figured out what the issue is specifically yet.

What's also interesting is that when the passenger side door opens the various interior lights don't come on (the one on the door, nor the dome lights). Not sure if that's related, could it be?
 
nsxotic911 said:
That's actually what I was thinking.. but the battery should be dead after a ride, correct? If I drive it for every day, it does ok.
Click to expand...

When I was in high school I drove an integra. The alternator went out and I didn't have the money to fix it, but I did have an extra battery. So I would charge one, drive it for a week or so, and then swap it out with the charged one. It was basically a full size R/C car. Young and dumb. You could drive it for a decent amount of time will a full charged battery. Especially a high quality battery like that. If you aren't using your headlights all the time that could easily be the issue.

Either that or I would guess a shorting wire that is killing the battery in a few days if you don't drive it every day. I've had that issue also. Pain in the A$$ to figure out where exactly the short can be.

Definitely keep us posted.
 
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DaveRMachin said:
I'm having exactly the same problem. We did the ammeter test and it says it's pulling 120ma, which I think is 2 or 3 times normal?

Looks like the fuse that runs the "interior lighting" circuit is the culprit, but we haven't figured out what the issue is specifically yet.

What's also interesting is that when the passenger side door opens the various interior lights don't come on (the one on the door, nor the dome lights). Not sure if that's related, could it be?
Click to expand...

I would say that they are directly related. A partial short to ground would account for the drain and perhaps keep the lights from lighting as well. Time for the careful study of the electrical schematic to see where the problem might be. I have not got one or I'd delve into it for you.
Good luck and keep us updated.
 
DaveRMachin said:
I'm having exactly the same problem. We did the ammeter test and it says it's pulling 120ma, which I think is 2 or 3 times normal?

Looks like the fuse that runs the "interior lighting" circuit is the culprit, but we haven't figured out what the issue is specifically yet.

What's also interesting is that when the passenger side door opens the various interior lights don't come on (the one on the door, nor the dome lights). Not sure if that's related, could it be?
Click to expand...

Not sure what the drain should be but this car seems to be higher then most.

Fuse 34 (interior light) in the under hood fuse box powers the passenger door courtesy light and part of the integrated control unit which in turn powers the driver door courtesy, footwell, dome and trunk lights. Also the power antenna and on some cars the tranceiver for the factory cell phone.

I would start by testing the passenger door switch, the instructions are in the repair manual. Could be a bad door switch keeping the light from working and maybe it is causing the ICU to draw more power.

Mike
 
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This should be easy to diagnose on the NSX because its electrical system is pretty simple. Theres really nothing that requires memory or can stay awake like on the newer cars. I would suggest doing a parasitic draw test. Get yourself a clamp on amp meter or you can use a volt meter to do this. Disconnect the negative battery cable and run your test leads from the post of the battery to the disconnected battery cable. (with a clamp on amp meter you can just clamp it onto the cable itself without disconnecting the battery). Precondition the vehicle by manually latching the hood latch so it thinks the hood is closed and latched. Open the doors and unbolt the door switches from the body. This tricks the car in thinking that its doors are shut. Do the same for the engine hatch. Now you can arm the vehicle with your alarm or by locking the doors so that the security system is activated, and you have access to all the fuse boxes on the car. Monitor the reading on the meter. I have never done a draw test on an NSX but I would say that 20-30mA is normal.

To give you an idea, a 1 amp draw will drain a battery overnight. So if you have an excessively high reading, then you know to chase down an electrical component that is staying "awake". If your reading falls in between the 1-30mA range, then I'd say it's the battery. If you have aftermarket electronics, I would troubleshoot those first. Removing fuses as Grybrd said will pinpoint the circuit that is causing the draw. Pull a fuse and monitor the reading. If the draw goes away, then you know it's on the circuit of the fuse you just pulled. If you have an ETM, the fuse to component index will show exactly what components are powered by each fuse. I usually just go down the list by disconnecting said components and seeing which one(s) are causing it.

Hope this helps!
 
Tech7042 said:
This should be easy to diagnose on the NSX because its electrical system is pretty simple. Theres really nothing that requires memory or can stay awake like on the newer cars. I would suggest doing a parasitic draw test. Get yourself a clamp on amp meter or you can use a volt meter to do this. Disconnect the negative battery cable and run your test leads from the post of the battery to the disconnected battery cable. (with a clamp on amp meter you can just clamp it onto the cable itself without disconnecting the battery). Precondition the vehicle by manually latching the hood latch so it thinks the hood is closed and latched. Open the doors and unbolt the door switches from the body. This tricks the car in thinking that its doors are shut. Do the same for the engine hatch. Now you can arm the vehicle with your alarm or by locking the doors so that the security system is activated, and you have access to all the fuse boxes on the car. Monitor the reading on the meter. I have never done a draw test on an NSX but I would say that 20-30mA is normal.

To give you an idea, a 1 amp draw will drain a battery overnight. So if you have an excessively high reading, then you know to chase down an electrical component that is staying "awake". If your reading falls in between the 1-30mA range, then I'd say it's the battery. If you have aftermarket electronics, I would troubleshoot those first. Removing fuses as Grybrd said will pinpoint the circuit that is causing the draw. Pull a fuse and monitor the reading. If the draw goes away, then you know it's on the circuit of the fuse you just pulled. If you have an ETM, the fuse to component index will show exactly what components are powered by each fuse. I usually just go down the list by disconnecting said components and seeing which one(s) are causing it.

Hope this helps!
Click to expand...

Tech, how do I test this...? I have a multimeter..
 

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