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Thread: Parasitic Drain - Battery Dead - Mazda 3

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    Default Parasitic Drain - Battery Dead - Mazda 3

    Hi all, this is my first time posting... never needed to before! I have been fighting with this car for weeks and I am ready to throw in the towel. I will try and summarize what I have done and experienced. I would greatly appreciate any support or suggestions... this thing is killing me.

    I have a 2009 Mazda 3 Hatch. It is completely stock in every way. I stopped driving the car for the snowy month of December waiting for snow tires to come in. It was my wife's DD until then with no issues. Upon getting the tires, I went to move the car to install tires and battery was dead. I jumped it with my truck and carried on. I checked out the battery (which was old) and it was frozen solid. I swapped it with a battery from one of my summer cars and the Mazda started fine. Then within 24-48 hours it would be dead again. This carried on for a week or 2 while I tried to figure it out.

    So, I performed a current draw test and with everything as normal with the key out, and all lights off; I was seeing about 150-220 mA draw. I opened up the main fuse box and pulled all the fuses with no real improvement. I also disconnected the alternator and there was no change. When I open the door, even with the lights off, there is a moment where it will jump up a bit, and then drops again once the door is closed, likely dash lights, etc. I then traced it back to the bolted down fuse labeled BTN. I reviewed the wiring schematics for the car to determine that the BTN fuse runs all the power locks, windows, marker lights, brake lights, horn, etc etc. The interior lights and radio are on a different fuse. The BTN fuse then feeds into the interior fuse box located in the pass. footwell. I pulled each fuse for the interior fuse box one by one and there was no change. I then pulled out every damn fuse at the same time, and still no change. So then I unplugged the entire interior fuse panel at the large connectors feeding into it, and finally the drain stopped.

    What I have determined is that there is no fused electronic device on the entire car that is causing this drain. It is always possible that there is a worn or damaged wire that is rubbing somewhere between the BTN fuse and the interior panel, but i would expect if this were true, that the current would be higher, and that I would have popped the BTN fuse. What I was hoping to know is if there is any other possible source of power. For example, even with all the fuses out, I can still see the little blinky light for the ignition lock... so the security device must still have power directly from the battery. Just to be safe, I swapped the battery with one from my other other summer car, and there was no change.
    Adding to this paradigm is that a (guessing) 40Ah battery with a 200mA drain should take about 8 days to drain. Assuming the car needs at least 50% capacity, it should be good for 4 days. Meanwhile, I worked on the car and changed the battery Saturday, and it started fine Sunday morning. On Monday morning, it was so dead that my wife said the key fob wouldnt unlock the door. So it seems to be intermittent as well.

    If I just walk away for a few minutes, it appears that the current draw is settling down around 150 mA... still too high, but stable. That is with all of the interior fuses pulled, and all of the main panel fuses pulled... and 100% of that drain is coming from the BTN line.

    Any thought, please let me know. Thanks for your time. It is greatly appreciated.

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    Default Re: Parasitic Drain - Battery Dead - Mazda 3

    How old are these batteries? There's no guarantee that they're ok. Your battery(ies) could have deteriorating plate connections within. Batteries like this go faulty once any bit of current is pulled from them.

    You're right, 150-200mA is excessive and I agree with your math.

    Back to the BTN fuse. The doorlocks on these cars use electrical feedback to ensure that they're locked. If one of the door locks isn't fully locking, the module might be trying to keep pushing power to it indefinitely. You could try removing electrical connectors from each of the devices on the BTN circuit to see if any of them are causing this. A similar situation would be a motor or solenoid winding that has a high impedance short in it, causing parasitic draw.

    Best of luck!

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