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Old 11-12-2019, 08:36 AM
Mgdpublic Mgdpublic is offline
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Diagnosing FSU as cause of parasitic battery drain?

Hey all,

My 2003 325xi battery was dying after 2 days of not using. I had the battery and alternator checked but the battery wasn't draining at the mechanic (left it there 3 days). After I got home, I realized after I turned off the car I heard a VERY faint whirring sound coming from center of dashboard. It sounded like a motor struggling with the rpms changing, but again, it was very faint. 2 days later the battery was dead again. I read a bit and thought it might be FSU so I pulled the 28 and 50 fuse which covers the blower (and one also covers the ac). The sound has now stopped. Btw it's prob important for you to know that my fans were fine, worked on low speeds and didn't vary. Is this still likely the FSU or might it be something else? I know very little about cars and didn't want to buy a new FSU and install if there's a chance it's not that. Given that sound, but the fans still working, how likely do you think its the FSU, and are their any other very simple diagnostics I can do to test if it's that? Thank you!
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