Parasitic battery draw?

2008 HONDA ACCORD
203,000 MILES • 2.4L • 4 CYL • 2WD • AUTOMATIC
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TWEBB101
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I've determined I have a parasitic draw in the system somewhere. When setting the multimeter to 500 mA setting, the meter reads .35* (last digit fluctuates). When I unplug the #15 fuse, in the engine compartment, the reading drops to 0.04* (last digit fluctuates). It's a 10a fuse and is labeled as "Back Up". I tried leaving that fuse in and pulling all the other fuses inside the car, on both panels, but nothing changed. Is there something else on that #15 circuit that I'm missing, or not checking?
Jan 9, 2024 at 2:16 PM
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AL514
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Hello, are you having a battery drain issue? And when testing do you have the door latches closed, so the interior light does not stay on? Fuse 15 (10amp) runs to quite a few things, can you verify when you have the fuse out, do you lose power to the Data Link Connector on pin 16? It looks to power that as well, just want to make sure we're looking at the correct circuit. And do you have any type of Navigation system, with a Hands-free link for your phone? Thats an option that can be on this circuit as well.
These are the aftermarket power distribution diagrams, showing Fuse 15 runs to the driver's side dash Fuse/Relay Box, and continues to a few other Junction connectors where you can unplug some connectors to see if the current draw drops off.

https://www.2carpros.com/articles/car-battery-dead-overnight
Jan 9, 2024 at 4:20 PM
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TWEBB101
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Yeah, the battery kept draining very quickly. Yes, I had the door switches depressed, so the dome light was off. I re-checked all interior fuses, but nothing changed. A common culprit that I kept seeing in some online forums was the master power window switch. I had to replace that a few months ago and thought that was when my electrical issues started. I unplugged that fuse, and nothing changed, but when I unplugged the master switch itself, the mA reading dropped like a rock to around 35 mA.
Jan 9, 2024 at 7:15 PM
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AL514
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So, some circuit that runs through the switch is your draw, do you have an amp clamp? You can check the current draw per wire with a low current amp clamp, instead of having a meter in series. You could even check the wiring at the rubber boot where the wiring passes through to the door from the body. So you can determine the wire color of the draw, then we can go by the wiring diagram for the door switch to see where the wire goes. It may be a door lock or window motor that can be the draw on any door since the driver's side door can control all of them.
Many of the doors these days have their own modules in them, along with a circuit breaker for the window motor, so its possible the window motor be stuck on and just keep tripping the breaker without blowing the fuse. I have the OEM driver door switch wiring diagrams pulled up I will post for you.

I also see CAN-B High and Low going to the driver's door switch, so it's on the network.
This is a 4 door model, correct?

It's possible that the door module keeps the network awake after the vehicle is turned off and locked up. Any module can do this really, since most everything these days are on networks.
Jan 10, 2024 at 1:09 PM
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TWEBB101
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I don't have an amp clamp, but if I can get one, do I just put each tiny wire from the wiring harness into the clamps and see what the mA readings are?
Jan 11, 2024 at 6:18 AM
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AL514
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Yes. Make sure you get one that reads DC current. I was shopping around, just looking at some and many were for AC current, designed for homes and such. So just make sure it can read DC current and it can read low mA's.
The Lower milliamp clamps usually have smaller jaws on them.
Jan 11, 2024 at 12:01 PM
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TWEBB101
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Just wanted to update this. I purchased a used part from eBay, but it was a genuine Honda part. Installed it and the mA reading only went up by .04. Battery is staying charged overnight and everything is working again. Definitely a bad replacement switch I purchased the first time.
Feb 12, 2024 at 8:17 AM
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AL514
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Thank you for the update, we rarely get to hear what the actual fix ends up being in most cases. So, the new master window switch was bad and that's what you replaced this time? Just be careful with eBay parts, they can say genuine Honda, but still just be a copied component. We can find part numbers for most everything through All Data or other service info places. So, looking up the OEM part number shouldn't be a big deal if you need. Glad to hear you got it fixed. A bad new part can really throw you for a loop, but it happens more and more these days, doesn't make the job any easier. But thanks again for letting us know.
Feb 12, 2024 at 11:05 AM