1997 E38 740i - very WEIRD electrical problem.

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  1. 1997 E38 740i - very WEIRD electrical problem. 
    #1
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    GregH's Car Details
    Model of Car:
    740I
    Year of Manufacture:
    1997
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    Saloon

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    Hi all,

    I'm new to the fora, but wondered if any of you experts could shed some light on a really wierd electrical problem with my 1997 740i.

    The problem started as the airbag warning light in the instrument cluster intermittently starting to glow, and the screen in the centre console not displaying properly, almost like a TV with a bad aerial connection.

    This got progressively worse, and started to effect other systems, such as the breaklights flashing when the break pedal was not depressed, and the interior lights turning themselves on while driving. Also the radio would not work, the cruise control and the steering wheel buttons would not work.

    My local garage told me that this was the ‘clock spring’ that sits inside the steering wheel that connects the moving part of the steering wheel to the non-moving car electrics.

    Accordingly I got a new one fitted, which altered the behaviour of the problem but not fixed it.

    What happens now is that sometimes I will get into the car, turn on the ignition and everything is OK, and it stays that way while the ignition is switched on.

    On other occasions the airbag warning light does not light during the instrument lights check, the radio and other systems (including the power steering) will not work. Sometimes this will rectify itself after a period of time.

    What is really bizarre is the recent discovery that if the problem manifests it can be sorted by pulling down either of the sun visors, and opening the slider over the mirror so that the lights should come on seems to make part of the electrical system ‘reset’, there is a bleep (normally heard when first turning the ignition key), the airbag light comes on for a few seconds, then everything works as it should.

    I am totally puzzled as to what this might be, and would love any ideas on where I should start looking for this problem.

    Thanks

    Greg.
     
     

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    #2
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    shamM3's Car Details
    Model of Car:
    318i
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    1997
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    sounds like a bad ground connection or something faulty in one of your modules. Have you had a look for loose/burnt wires?
     
     

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    #3
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    GregH's Car Details
    Model of Car:
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    I've taken a bit of a look around, but everything looks OK.

    Just found this post though http://www.bimmerforums.co.uk/forum/...g-light-t1888/ which sounds very similar to my problem, and says that the ignition switch is the problem, so will start there.
     
     

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    #4
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    shamM3's Car Details
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    Yep Greg, looks like your ignition switch then after reading up on that post. I think you should get it booked in and get a diagnostic test done.
     
     

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    #5
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    Kevin Whittaker's Car Details
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    Reading your first post I have to say it sounds like a faulty ignition switch

    Funny things these electrical problems sometimes
     
     

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    #6
    Dr of BMW gildersol's Avatar
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    This is a common problem on these cars. The symptoms point to a faulty ignition switch. Believe it or not the sun visor bit is the tell tale sign. A new electrical switch block should fix this.
     
     

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    #7
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    GregH's Car Details
    Model of Car:
    740I
    Year of Manufacture:
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    Hi all,

    Been a while, but I actually got a replacement ignition swithc fitted today, and it appears to have cured the electrical problems that I was suffering.

    Quite why opening the sun visor made things work I'll never know, but it's a useful trick to be aware of :-)

    Greg.
     
     

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    #8
    Dr of BMW gildersol's Avatar
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    Good to know it's fixed
     
     

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