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Thread: Electrical issues with 740i

  1. #1
    Join Date
    Apr 2008
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    BMW E32 735i

    Electrical issues with 740i

    So a friend of mine, gave me his car to take a look at the electrical system, and after some research I'm quite lost.

    1. There is some current draw when car is locked - after some research I found out it was via fuse 30. But on fuse 30 there are quite some different modules connected - Central locking, door lock heating, power windows, sunroof etc. However I cannot find anything not working in order to isolate the issue.

    2. The IHKA is not working at all, like there is no power to it, no matter the fact, that all fuses are perfectly fine.

    Overall, both issues are pretty strange to me, so if someone could drop some ideas, I would be thankful.

    BR
    Stoyan

  2. #2
    Join Date
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    735iL - 1989
    shogun has written that the door lock heater has caused troubles like this.

    How much current is flowing from the battery when the car is quiet? You can reach in through the rear window with the doors all closed to read your ammeter (connected in the battery Ground cable.)

    The magnitude of the current flow is a clue as to the cause of the drain.

  3. #3
    Join Date
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    BMW E32 735i
    When car is in sleep mode - 0,07A or 70mA. When fuse 30 is removed it drops to about 30-40mA.
    However there are a lot more items powered through this fuse, therefore looking for advice.

    BTW found out there is some water condensation in the trunk, which makes me think, there could be some issues with the soft close module.

    Besides from those issues, the rear defroster fuse has blown again, burning the plastics around it again. This was fixed two years ago, and I still have not found any particular causes for this issue.
    Last edited by StoyanG; 06-13-2017 at 12:25 PM.

  4. #4
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    So there is an extra 30 ma to be explained.
    The candidates are all ZKE - Central Locking, Power Windows, Sunroof, Central Body Electronics.
    You can exclude Door Lock Heating and Interior Lights because they draw too much.

    F30 is shown on Page 5120-02, 5126-02, 5410-03, as feeding RM X258 pin 15 only. On page 6100-00 is shown this same circuit flowing out X258 pin 5 to X332 pin 1 on the GM. Current flows to the various loads only because relays inside RM are energized.

    So F30 feeds relay coils and digital logic in GM and RM. I would suspect that a defect inside the GM is drawing the extra current.


    BTW, I have found that water in my trunk can be fixed by tightening the latch adjustment nut. I do not have soft close.
    BTW, I think that the burning rear defroster fuse is caused by poor contact at the fuse itself. Best to use a high quality external fuseholder as used in car audio.
    Last edited by E32FAN; 06-13-2017 at 01:46 PM.

  5. #5
    Join Date
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    Did some more research and managed to fix the IHKA issue - found out that the ground nut under the dash has become loosen. This seems to helped with the sound quality issues when listening to CD's, since there were some additional sounds messing the music.

    Further more - the current drawn when car is in sleep became 80mA, which is quite strange. Non the less I've changed all electrolytic capacitors in the GM module, since for all those years they might be causing some issues.
    I'll continue the research tomorrow morning, since here it's quite late already.

    Quote Originally Posted by E32FAN View Post
    So there is an extra 30 ma to be explained.
    The candidates are all ZKE - Central Locking, Power Windows, Sunroof, Central Body Electronics.
    You can exclude Door Lock Heating and Interior Lights because they draw too much.

    F30 is shown on Page 5120-02, 5126-02, 5410-03, as feeding RM X258 pin 15 only. On page 6100-00 is shown this same circuit flowing out X258 pin 5 to X332 pin 1 on the GM. Current flows to the various loads only because relays inside RM are energized.

    So F30 feeds relay coils and digital logic in GM and RM. I would suspect that a defect inside the GM is drawing the extra current.
    Thanks for the nice reply. I've also checked those in the ETM myself, but this didn't give me a particular idea what to look for next.
    Maybe the best thing to do is to start unplugging different items one by one - Soft close, Central locking etc.
    Last edited by StoyanG; 06-13-2017 at 03:54 PM.

  6. #6
    Join Date
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    BMW E32 735i
    Still have not found anything suspicious. Checked RM, GM, Softclose etc - nothing wrong.

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