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Thread: 96 850i electrical gurus needed / windows going down randomly

  1. #1
    Join Date
    Mar 2005
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    '85 M635csi, '84 545i, 88 M3

    96 850i electrical gurus needed / windows going down randomly

    Hey guys,

    My friend has a 1996 850i that has us completely stumped. For the last 4-5 months we (me and mostly a bmw tech who used to work on these at the dealer) have been trying to figure out why the auto open convenience feature activates at completely random times. We have a 95 840i and a 91 850 parts/donor car and we have swapped and tried just about every module including:

    - general module
    - relay module
    - driver door handle assembly
    - door modules
    - and countless other items

    The windows/sunroof open at random. There is no rhyme or reason to it. Sometimes they will do down and after putting them back up, they will do down again in 5 minutes. Sometimes 3 days will pass until they go down. Sometimes you're driving and all of a sudden all everything starts opening. Sometimes it happens when the car is parked. If you disconnect the driver door harness the other windows and sunroof will still open. It doesn't help that there doesn't exist an ETM after 95 and I'm guessing there is one small minute detail that they changed in 96 that we haven't looked at yet?

    If there wasn't a need for the windows to go down to open the doors we'd just install a master bypass switch...but that's not the case.

    Wondering if anyone has heard of a similar problem? Tough to believe that the parts car would have the same issues as this one. Maybe related or unrelated but when you try to lock the car with the remote the car will lock, and immediately unlock.


    Thanks!

  2. #2
    Join Date
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    do the windows open first, then the sunroof?
    '91 Dinan 860 Stage III (new 6L engine)
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  3. #3
    Join Date
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    '85 M635csi, '84 545i, 88 M3
    So if the car is sitting (it just went down an hour ago) the car horn chirps like if you were unlocking the car and then the windows and sunroof open at the same time.


    Sent from my iPhone using Tapatalk Pro

  4. #4
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    6.5 second 69 Camaro
    Sounded like a seized in the far right position or faulty door lock until you said the horn chirped, Never heard that one. The alarm factory?

  5. #5
    Join Date
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    99 840ci Sport Indv
    Yes, that certainly sounds like an alarm issue - either a rotten after-market one stuffed in somewhere or the OEM version fizzling out - often due to the rechargeable battery splurging out its innards...
    Timm..2007 E64 650i Individual Sport..1999 E31 840ci Individual Sport..ex owner of 2000 E38 740..1999 E38 740i V8 M62..1998 E38 735i V8..1993 E32 730i V8..1988 E28 518i


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  6. #6
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    Quote Originally Posted by Timm View Post
    Yes, that certainly sounds like an alarm issue - either a rotten after-market one stuffed in somewhere or the OEM version fizzling out - often due to the rechargeable battery splurging out its innards...
    I'm pretty sure the problem persisted with the factory alarm disconnected...I'll try that again to see what happens.

    Also remember that we swapped the door lock assembly with one from another car with same issues.

  7. #7
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    On second thoughts - could this be a problem with the remote locking receiver - or even a faulty key that is sending out the unlock signal. The receiver is in the rear-view mirror and can be disconnected after unlocking the car - that would certainly do it!
    Timm..2007 E64 650i Individual Sport..1999 E31 840ci Individual Sport..ex owner of 2000 E38 740..1999 E38 740i V8 M62..1998 E38 735i V8..1993 E32 730i V8..1988 E28 518i


    My BMW Repair YouTube Channel
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  8. #8
    Join Date
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    91 Dinan860 & 91 850 6sp
    Passenger door lock switch.
    '91 Dinan 860 Stage III (new 6L engine)
    '91 Dinan 850 TT stage III (brand new engine) 21st Century Tech meets 18th Century Dinan...
    '91 850i 6sp (mint) (sold)
    '90 Dinan 750iL TT stage III (Guido - The Beast)
    '94 850 CSi The Detroit Auto Show car (restored to factory perfect) (sold)
    '96 850Ci, The George Carlin car
    ''73 3.0 csi, '08 535i, '03 X5 4.6is
    ...and a few other non BMW cars

  9. #9
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    A friend has had a similar problem, which was referred to a ground fault in the lower part of the a-pillar where the cables go to the door, may be an idea to check these cables and connections.

  10. #10
    Join Date
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    '95 840Ci, '06 730d
    Sorry to hijack; Timm, where is this rechargeable battery? Is it part of the siren?

  11. #11
    Join Date
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    99 840ci Sport Indv
    Yes, it is in the same unit as the siren.....
    Timm..2007 E64 650i Individual Sport..1999 E31 840ci Individual Sport..ex owner of 2000 E38 740..1999 E38 740i V8 M62..1998 E38 735i V8..1993 E32 730i V8..1988 E28 518i


    My BMW Repair YouTube Channel
    My Current 840ci Sport Individual
    My Current 650ci Sport Individual
    My E31 Repair and Information Website
    My E38 Repair and Information Website
    My E63/E64 Repair and Information Website

    Chase - Heroes to a generation

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