I this is a long shot……………
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URL: https://www.allischalmers.com/forum/forum_posts.asp?TID=209122
Printed Date: 27 Nov 2025 at 1:49pm
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Topic: I this is a long shot……………
Posted By: Lars(wi)
Subject: I this is a long shot……………
Date Posted: 27 Nov 2025 at 10:44am
but, is anyone here familiar with BMW’s? Son has a 2015 335i, when the weather turns cooler(under 50 deg F., the battery drains dead. Several battery swaps over the years, has not solved the issue, numerous trip to the stealership temporarily fixes the issue. Last week when I was at his place it happened again, cool day, jump started the car, did his route for the day, came home, shut it off, couple hours later, battery dead as a door nail. Hooked up the charger, after a few minutes, the electric water pump turned on. I know the electric water pumps on these cars are problematic, has anyone conquered this issue. I know BMW’s are an electrical nightmare. Any help/suggestions, or some tanerite would be greatly appreciated.
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I tried to follow the science, but it was not there. I then followed the money, and that’s where I found the science.
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Replies:
Posted By: jaybmiller
Date Posted: 27 Nov 2025 at 11:37am
no ,but it sounds like 'something' is turning on,draining the battery when <50*F. Maybe a seat heater,windshield heater or some other 'hightech' item ?? I'd put an ammeter between battery and 'the rest of the car' to see how much current is being drawn. Any lights on ( under the hood ?). Newer cars have 'CANbus' ballast resistors and they WILL kill a battery. Maybe the alternator is 'kinda' bad ? If ammeter say power is being used, start pulling fuses, one at a time, to locate WHICH circuit it is. Please report back with any new information !
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3 D-14s,A-C forklift, B-112
Kubota BX23S lil' TOOT( The Other Orange Tractor)
Never burn your bridges, unless you can walk on water
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Posted By: AC7060IL
Date Posted: 27 Nov 2025 at 12:03pm
Not familiar with particular model. Google it? Search yr model issues & watch internet light up about issues. Good luck.
Below is a link of my find from ;
“2015 335i battery issues” search
Could be it has “on demand” alternator charging?? If so, it’s battery’s ground terminal sensor may be defective? A temp fix ~ delete that sensor for a direct ground. That will produce a constant charge alternator to assist the moment. Get new sensor for long term fix.
https://www.reddit.com/r/BmwTech/comments/11x4enb/2015_bmw_335i_battery_discharging_while_stopped_i/" rel="nofollow - https://www.reddit.com/r/BmwTech/comments/11x4enb/2015_bmw_335i_battery_discharging_while_stopped_i/
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Posted By: Lars(wi)
Date Posted: 27 Nov 2025 at 1:38pm
We have noticed the electric water pump will continue to run after turning off the engine, even after the engine cools. Internet has posted different solutions, we put a new battery a hour ago. Water pump turned on. Some solutions include; unhook battery for several hours to allow ECU to reset, the water pump is faulty ECU is sending signal to w. p. to stay from faulty reading from temp sensor
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I tried to follow the science, but it was not there. I then followed the money, and that’s where I found the science.
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