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Hello guys, soo ive been constanly having battery issues with my car for the last year. Soo now whenever i stop driving the car for a while I disconnect the negative terminal to stop the battery from draining. Now my check engine light is on. And i read my codes and it is a P1515 code. I also read my codes on the bmw scanner and im getting a bunch of random stuff that doesnt seem important. So i looked up P1515 solutions and im getting alot of mixed reviews/answers.
 

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What from the past year have been your battery issues? Is the battery old or new? Is the alternator and it's voltage regulator functioning properly? Is there a added component such as an elaborate amplified stereo system as a potentially unknown voltage draw? Old batteries make alternators function near full-time..thus lessening their life span as the brushes within the regulators wear exceedingly fast...They actually produce faster voltage towards their end..(spring direct on armature)
 

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What from the past year have been your battery issues? Is the battery old or new? Is the alternator and it's voltage regulator functioning properly? Is there a added component such as an elaborate amplified stereo system as a potentially unknown voltage draw? Old batteries make alternators function near full-time..thus lessening their life span as the brushes within the regulators wear exceedingly fast...They actually produce faster voltage towards their end..(spring direct on armature)
The battery was draining after a couple days of no use. So i started by buying a new battery. No change soo i began to just undo the negative terminal. Yes i do have aftermarket radio and i tried to unplug the fuse for radio and stil drive car with negative terminal connected but that didnt help either. And alternator still seems fine, charging at correct voltage.
 

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The battery was draining after a couple days of no use. So i started by buying a new battery. No change soo i began to just undo the negative terminal. Yes i do have aftermarket radio and i tried to unplug the fuse for radio and stil drive car with negative terminal connected but that didnt help either. And alternator still seems fine, charging at correct voltage.
Did you buy a cheap CHINESE battery?...They are worst..and give wrong info when checked with digital battery checkers...even with SNAP-ON battery checkers. More terrible batteries are on the market today than ever...Even cheap WalMart batteries fall into question more so lately.
 

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Did you buy a cheap CHINESE battery?...They are worst..and give wrong info when checked with digital battery checkers...even with SNAP-ON battery checkers. More terrible batteries are on the market today than ever...Even cheap WalMart batteries fall into question more so lately.
Mmm i actually did buy the walmart everstart or something like that. They did not have the h7 which is the direct replacement I believe, so i had to get the h8 which is a little bit bigger with more CCA
 

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Discussion Starter #7
The FSR, aux electric fan or the heater valve are suspects for battery drain to no start on a good battery in a short time.
I replaced the FSR as well but i will do test on the aux fan , and was wondering how to test the heater valve ?
 

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The FSR, aux electric fan or the heater valve are suspects for battery drain to no start on a good battery in a short time.
OLD CAR SYNDROME............Yes..in this case it means higher than manufactured resistance...thus a failing fan that uses, demands, more dc! Call it a domino effect...ultimately all players come to the same corner!
 

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I replaced the FSR as well but i will do test on the aux fan , and was wondering how to test the heater valve ?
You can disconnect it when you park the car. See if that eliminates the battery drain. In the meantime about an hour after you've shut off the car go out and feel the heater valve - see if it's hot - if it's shorting internally it will be hot.

For the aux fan drain it is much more difficult. Often the fan does not spin but the final output (Bosch fan box) drains power. It will be warm long after the car has shut off. Again thru process of elimination, try unplugging the pigtail connector at the shroud to see if that prevents the overnight drain ( you'll have to test one component at a time tho)

All three of the items I suggested are unlike most other electrical components on this car in that they are live at all times even after the 16 minute to sleep cycle.
 
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