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    Battery drain - aux fan?

    1999 E39 528i - I've got an intermittent drain on my battery which has caused it to be unable to start the car in the morning twice in a week (but NOT every day!). Battery is good, alternator is good per my indy mechanic. He suggested that it might be a problem with the electronics in the aux fan. Any ideas?


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    Member No: 4328 jimlev will become famous soon enough jimlev will become famous soon enough jimlev's Avatar
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    It could be that or many other things (m)

    Looking at your IP address I'm guessing you are in MA. Why don't disconnect the aux fan and see if the problem stops. You don't need an aux fan around these parts now.
    Could also be the the FSU. You could check the drain on the battery after all modules go to "sleep". If the current draw is higher than ~30ma start pulling fuses until you find the circuit that is defective.

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    rle2002bmw
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    UPDATE: Re: Battery drain - aux fan?

    More information - I put a current probe on the battery and discovered that the current drain immediately after shut-off wanders between 50mA or so and 8A. It does not stabilize until about 35 min. after turning off the ignition - and then it's about 50mA. My indy mechanic says that the stabilization time whould be about 15 to 20 minutes but he has no idea what else to look for, if anything. I suspect that my problem is that sometimes whatever-it-is that's pulling current after shut down is sometimes not completely shutting down. Any ideas? TIA!

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    Start pulling fuses one at a time until you see (m

    the current drop. All modules should go to sleep after 16 min. You will see the trunk light go out after everything times out. This is when you want to start pulling fuses. Start with the trunk fuses, if you don't find anything move to the fuses above the glove box.
    After you pull a fuse and don't notice any change, if you stick it back in it could wake up a module. If this happens (might not) you will have to wait for it to time out again.
    The big current draw items are the Aux fan, the FSU, general module, LCM.

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    FWIW those are the same symptoms I had when > >

    my FSU failed. The current drain was very erratic and would spike above 5A for brief periods of time. This occurred immediately after shutdown but before the electrical system went to 'sleep'. You may find it easier to unplug the FSU than it is to pull the fuses which feed the FSU. There were times when the current drain would fall off to <20ma as you would expect but that didn't mean it stayed there. After a couple of non-start occurrences, I ran the problem down to the FSU. Replaced with the new, improved design and trouble gone. If it is determined to be the FSU, stay away from the "bargains" available on eBay. They seem to have a very short half-life.



    Filehorse
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    2002 525i Steptronic Sport/Premium | Build Date: 05/02
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