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Steve
Steve, BMW Expert
Category: UK Car
Satisfied Customers: 23602
Experience:  BMW Expert
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I've got a mysterious battery drain on mu E39 530d Touring.

Customer Question

Good morning! I've got a mysterious battery drain on mu E39 530d Touring. The FSU has been replaced, disconnected CD changer and telephone but the drain is still going on.. Anyy ideas?
JA: Have you tested the battery with a voltmeter? And can you see if it's leaking or not?
Customer: Yes, fully charged 12.6v It's 18 months old
JA: Are you fixing your Touring yourself? What have you tried so far?
Customer: Yes I am trying to fix it. I've replaced the FSU Disconnected the battery overnight and discovered there was nog drain when disconnected
JA: Anything else you want the mechanic to know before I connect you?
Customer: Also disconnected the navigation/DSP and that didn't help either
Submitted: 6 months ago.
Category: UK Car
Expert:  Steve replied 6 months ago.
Hello and welcome,
My name is ***** ***** it will be my pleasure to assist you today.
What testing has been carried out?
Also can you please clarify what exactly your question is about this? Do you just want suggestions as to what the possible cause is?
Customer: replied 6 months ago.
Helle Steve, I've got a battery drain on my E39 530d touring. The FSU is replaced by an original new one, telephone, CD changer an navigation are disconnected but the battery is still being drained. When i disconnect the battery overnight it is still fully charged when connected to the car again. The battery is 18 months old and OEM BMW. The alternator is also new for 6 months. When running the alternator gives 14.2 volts
Expert:  Steve replied 6 months ago.
I will provide an honest answer. I trust this will be appreciated. Please remember that a low rating PUNISHES me for being honest and that I receive nothing for my time until a positive rating is clicked.
Thank you for your attention to the rating requirement.
The only other items that are remotely likely to be the cause are the electric engine fan or the abs module or the srs module
You can try those components one by one, but In order to determine the cause of this drain with certainty, you will need to unhook the negative battery cable and hook up an amp meter and measure draw after the car is locked and has sat untouched for 20min (this is when it is supposed to be in "sleep mode"). If there is more than about 50ma of draw at this point, you will need to pull fuses one by one until the draw stops. Whichever fuse stops the draw is the problem circuit and you have found the issue
Please let me know if you have further questions. Please do not forget to click a positive rating as this is the only way I receive credit for my answer, thank you. Best wishes with your vehicle.