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Thread: Battery drain in central locking/power windows circuits

  1. #1
    Join Date
    Feb 2006
    Location
    Blackburn, Melbourne, Australia
    Posts
    13

    Default Battery drain in central locking/power windows circuits

    I have a problem with the battery charge being depleted to a point where the car won't start - the battery voltage drops to 10 volts or less and nothing happens when the key is turned to engage the starter, although everything else still operates.

    I have found that when pulling out the 7.5A fuse under the back seat that is in the power windows and central locking circuit, the current draw on the battery (with everything off) drops from 240ma to 20ma. These things have been operating fine.

    The alarm system intermittently beeps while driving, flashing the red LED on the dash grille. Does this indicate a fault in the locking system and could these two things be related?

    Any help as to were to start loocing for the fault would be greatly appreciated!

    Colin,
    Melbourne Australia
    1990 535is manual.

  2. #2
    Join Date
    Jan 2005
    Location
    Scotland
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    119

    Default

    This may not be the case but a lot of the electrics stay alive for about 15 minutes after the ignition is turned off - during this time the current flow from the battery can still be quite high (in the order of hundreds of milliamps for the windows, locking etc); after that it should drop to below 50mA.

    If you are out of the 15 minute window then pulling the fuse for the windows and locking might indicate a fault in this behaviour.

    Stu.

  3. #3
    Join Date
    Mar 2006
    Location
    Great Britain
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    446

    Default

    Why not leave the 7.5A fuse pulled out for the moment, and also disconnect the alarm system? Assuming that this stops the battery voltage depletion, you can then reconnect them one at a time, at which point it will be clear which is causing a problem.

  4. #4
    Join Date
    Nov 2005
    Location
    New Jersey USA
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    Default

    I had the same problem... for a long time I kept getting a battery drain. I finally traced it to the central locking so I too pulled the fuse under the rear seat.

    Finally poked around and found this in the drivers door:





    Had to replace the entire door wiring harness, now the car drives like new.

    Check to see if your wiring is fried... you never know.

  5. #5
    Join Date
    Feb 2006
    Location
    Blackburn, Melbourne, Australia
    Posts
    13

    Default

    Quote Originally Posted by stu1
    This may not be the case but a lot of the electrics stay alive for about 15 minutes after the ignition is turned off - during this time the current flow from the battery can still be quite high (in the order of hundreds of milliamps for the windows, locking etc); after that it should drop to below 50mA.

    If you are out of the 15 minute window then pulling the fuse for the windows and locking might indicate a fault in this behaviour.

    Stu.
    Thanks Stu

    I have previously found the post on the forum with the procedure for checking the 'closed circuit current measurement' and despite not having followed this yet, I am assuming the the current drain continues beyond the 15 minutes as the battery does go flat.

  6. #6
    Join Date
    Feb 2006
    Location
    Blackburn, Melbourne, Australia
    Posts
    13

    Default

    Quote Originally Posted by pingu
    Why not leave the 7.5A fuse pulled out for the moment, and also disconnect the alarm system? Assuming that this stops the battery voltage depletion, you can then reconnect them one at a time, at which point it will be clear which is causing a problem.
    This sounds reasonable thanks Pingu. How do you disconnect the alarm system?

  7. #7
    Join Date
    Feb 2006
    Location
    Blackburn, Melbourne, Australia
    Posts
    13

    Default

    Quote Originally Posted by spyrot1
    I had the same problem... for a long time I kept getting a battery drain. I finally traced it to the central locking so I too pulled the fuse under the rear seat.

    Finally poked around and found this in the drivers door:





    Had to replace the entire door wiring harness, now the car drives like new.

    Check to see if your wiring is fried... you never know.

    Thanks Spyrot1. I have seen your thread about your problem and I don't think I have as drastic a fault as that, as the fuses don't blow and everything is still operating normally.

  8. #8
    Join Date
    Dec 2003
    Location
    Wellington,New Zealand
    Posts
    3,868

    Default

    it doesnt have to be as bad as that.I would say you do have some kind of "short circuit" tho....
    Gone but not forgotten

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