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Thread: 1999 528i e39 Battery Drain isolation

  1. #1
    Join Date
    Apr 2015
    Location
    Canada
    Posts
    10
    My Cars
    1999 528i

    1999 528i e39 Battery Drain isolation

    Battery goes dead after about 3 days. Pain trying to use an ammeter to isolate circuit by elimination removing fuses due to all the stuff that runs when off and the currents can be very high on some circuits.

    Reading threads, common culprit is the FSU or the Aux Fan. I assumed FSU as that seemed more common.

    I used the built in voltmeter on the dash (With key on the on position, hold odometer reset for 5 secs till 'test' appears, press repeatedly till '19' appears, what till '0', press repeatedly till '9' appears. Will then display voltage.)

    Right after driving the car giving alternator time to fully charge the battery, voltage reads about 12v. After about 24 hrs of sitting there, reads 11.4v.

    I the drive again till full battery, check back to 12v. I then pull the heater blower/FSU fuse (#76 40A fuse) located behind the glove box. Shut it all down, leave it 12 hrs and recheck... Down to 11.6v... so unlikely the FSU.

    Do it all again, but now put FSU fuse back and this time pull the Aux Fan fuse (#75 50A fuse) right next to FSU/heater fuse. Shut it down, leave it 12 hrs and voila, recheck shows 12v! It must be the aux fan circuit somewhere...

    To double check, I unplugged the put the fuses back in and unplugged the aux fan via the 3 wire connector just in front/left if the fan when looking at the car. Bit tricky to unplug. Redid my test and voila... 12v, all good.

    Now I need to figure out what it could be... likely the resistor pack or controller. But relatively easy way to isolate.

    Will update when all fixed.



    Sent from my ONE A2005 using Tapatalk

  2. #2
    Join Date
    Feb 2011
    Location
    Fairfield, Connecticut
    Posts
    1,339
    My Cars
    '98 540i '01 540i 13 E70
    Any updates--got a real headache of a battery drain on my e39 540i...
    Thanks!

  3. #3
    Join Date
    Jul 2016
    Location
    Chicago, Illinois
    Posts
    3,842
    My Cars
    are slow
    FSU first thing's first.

  4. #4
    Join Date
    Apr 2015
    Location
    Nor cal
    Posts
    36
    My Cars
    2001 540i/6
    Just take the time to trace it by fuse elimination. Will be the most accurate in your case.

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