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Thread: Totally insane electrical problem

  1. #1
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    Totally insane electrical problem

    Hello friends of the BMW,

    I have a problem with my wife's 525 Touring (2003, FL) that I can't explain; actually seems completely absurd... But first things first:


    From time to time, the vehicle's electrical system does not seem to switch off after leaving the vehicle. Then the next morning the battery is completely empty, so that not even a little lamp or something like that lights up. The battery voltage is then often in a deadly range below 6V for the battery. So far, so bad... I'm still looking for the problem...
    In this context, I now always connect the vehicle to a charger (14V / 7A DIY) in the evening so that my wife, who is dependent on the vehicle due to a disability, does not have any problems in the morning. This also worked without any problems until recently, when this unloading problem hit our daughter, who had borrowed the car.
    We always connected jump starters and/or the charger to the + pole on the engine cover and the bolt provided for this purpose on the left dome bearing. That's what it says in the user manual.
    But after the incident with our daughter, it seems that the ground connection from the top mount to the body is completely broken?!?
    I checked today:
    There is a perfect connection from the ground bolt to the other two bolts of the top mount. So they all have contact with the sheet metal of the dome bearing. But if I measure from there, e.g. to the engine block or other ground points (the blue arrows), the connection is high-impedance. The sheet metal of the dome bearing has no connection to the vehicle mass all around...


    How can that be? That's completely impossible?!??


    FL-electric problem.jpg
    This picture is "stolen" out of the internet. I forget to take a own one and now it's dark outside...
    I have insert the red- and blue arrows (the nice ones); the ugly are from the original...
    Last edited by M*I*B; 01-31-2023 at 05:15 PM.

  2. #2
    JimLev's Avatar
    JimLev is offline Artifically Aspirated Moderator
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    Have you checked the ground strap from the pass side motor mount bracket to the frame rail?
    You’ll need to jack the car up, remove the lower engine cover to access both ends of the ground strap.

  3. #3
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    Hi Jim,

    thanx for the hint. That I will do shortly with the EndoCAM. It's always raining here and freezing cold; camera is better and healthier than floor exercises for an old one like me

    ... hmm ... ... because I'm thinking about it right now:Would that make a difference? The starter gets its ground from the engine block and it can be started (with a full battery) without any problems. And since the negative of the battery in the rear is connected to the chassis via a ground strap, the connection between the battery -> chassis -> engine-block must be intact.
    If that's the case and I'm not missing something here, then it would mean that the left front chassis parts (inner fender, dome bearing sheet, peripherals) are no longer connected to the rest of the chassis. And since this vehicle is not glued but mainly spot-welded, that would mean that all welding points are open...
    It's hard to imagine...


    Can you follow my train of thought? My english sucks... sorry

  4. #4
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    Thank you for posting! Your post will not be visible until a moderator has approved it for posting.
    ... what ?!

  5. #5
    JimLev's Avatar
    JimLev is offline Artifically Aspirated Moderator
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    Quote Originally Posted by M*I*B View Post
    ... what ?!
    Until you have 10 post one of us Mods needs to approve them. It’s one way to limit spam.

    You won’t be able to see enough with a camera.
    You’ll probably find a lot of corrosion on both ends of the ground strap where it connects to the body and motor mount bracket after you remove the bolts.

  6. #6
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    Today I checked the ground connection on the engine block. Amazingly, there are two here: one on the left, one on the right, bridging the gumblock engine mount. They don't look 20 years old either, but quite "new". They were probably installed by the previous owner; all the better.
    I measured both individually. Not with an ohmmeter, but by applying a constant current of 10A between motor block and mass point on the axle suspension. Then I measuring the voltage drop across (~8mV). According to this, both ground straps are in very good condition and have excellent contact with the engine block and the chassis.
    So, as I've pointed out, that's not the problem. So it was a superfluous effort if I hadn't been able to repair the defective line from the oil level sensor at the same time.



    So the question remains, how is it possible that the left inner fender and the sheet metal dome bearing have no contact with the vehicle mass/chassis?!

  7. #7
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    Quote Originally Posted by M*I*B View Post
    ...So the question remains, how is it possible that the left inner fender and the sheet metal dome bearing have no contact with the vehicle mass/chassis?!
    Right. That's impossible. So there must be another reason.

    Those might include:
    1) Something odd about your meter or your test approach. Check everything and repeat. Try another meter and a slightly different approach.
    2) There's an unexplained short that's causing your battery to die overnight. That could also be causing strange readings.
    2a) Strange readings might also give you a clue for finding the short. I'd try disconnecting a battery lead and checking continuity to various different ground sources. Then I'd test continuity (resistance) to the positive side too.

    I know it's frustrating, but physics is ultimately logical. There's always a reason, we just have to find it.

    For example, there might be (probably is) paint between the nuts and the fender. The bolts might also be insulated from the fender. Check readings at other locations, look for a place where the paint is missing on the fender, or make a small scratch to bare metal and test there.
    Last edited by R Shaffner; 02-02-2023 at 03:43 PM.

  8. #8
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    I know it's frustrating, but physics is ultimately logical.
    ...that may be true, but depends on what you consider logic...


    What I forgot to mention is that I have been working in electronics (development) and mechanical engineering for over 40 years. Therefore, one may concede that I am more than experienced in dealing with measuring devices and measuring arrangements. I also work on vehicles (vintage motorcycles, cars and excavators) for just as long; sorry for not mentioning that before...


    In this context, we can safely forget point 1.
    Point 2 is a different topic. As far as I have been able to determine so far, the board system sometimes does not switch off, even though all doors are definitely closed. But I'm still working on the problem.
    Point 2a is planned for the next few days when it doesn't rain ^^


    ... paint between the nuts and the fender. ... Check readings at other locations, look for a place where the paint is missing on the fender, or make ...
    I had already checked that, but your hint gave me another idea, which I will check tomorrow (if it doesn't rain).
    I'll report as soon as I have a/no result...

  9. #9
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    I wasn't trying to challenge your background or ability. Just supporting your logic.

    For example, I've recently had meters give odd readings a day or two before their batteries died. And a few months ago, I thought I was going crazy with a problem similar to yours, when I discovered that one meter wand would lose connection internally when the tip was pressed against something just the wrong way. So I'd get voltage between good contacts, then I wouldn't, then I would again.

    And I recently had a 12v battery (on a platform lift) that had acquired a negative (opposite) charge when it was connected in series with another battery and a 27 volt charger. I didn't know that was possible.

    So mostly I'm just saying hang in there -- odd things can and sometimes will happen.
    Last edited by R Shaffner; 02-02-2023 at 05:47 PM.

  10. #10
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    I wasn't trying to challenge your background or ability. Just supporting your logic.
    I didn't want to impute that to you either; that's exactly how I understood it.

  11. #11
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    Quote Originally Posted by M*I*B View Post

    From time to time, the vehicle's electrical system does not seem to switch off after leaving the vehicle. Then the next morning the battery is completely empty, so that not even a little lamp or something like that lights up. The battery voltage is then often in a deadly range below 6V for the battery.
    Most of this thread has been about a possible faulty negative jump point in the engine bay...Who cares? there are many other good grounds in the engine bay..

    Don't you want to focus on the main problem?

    When the car fails to turn off - maybe the interior lights fail to go out or some other issue draining your battery - why don't you simply measure the amperage draw at the fuse panel to try to determine which module is causing this issue?

    I suggest testing to identify a parasitic draw. But I might also do a few things...If it happens regularly, I would shut off the car, but stay in the car and don't open the door and see if it shuts off. I might also consider exiting out of another door just once to test which door....I know this is not possible for your wife.

    It sounds to me that one of the door sensors (driver's door) is not reading a closed door properly? I think it is a Hall-type sensor in the latch, but I am not sure. I had something similar happen on my E53 X5, but only in very cold weather.
    Last edited by effduration; 02-04-2023 at 07:52 AM.

  12. #12
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    Little update...


    @effduration is right, but only partially. Who says this "weird" host problem isn't related to the other problem?
    I haven't really been able to pinpoint the mass problem until now. Relocating the connection would only be a symptom fight. So I have now put a ground strap from the strut bearing to the engine block; I had a long strap left over from my excavator. So at least the mass is completely available again.
    So far the second problem has not recurred. But that shouldn't mean anything. It was also the case before that there were no problems for weeks and then from one day to the next in the morning the battery was empty.
    I used my good clip-on measuring device to monitor the switch-off of the on-board electronics for hours... open the door, close the door, wait... open an other door, close the door, wait... and so on; no abnormalities.
    So I got a cheap clip-on measuring device with Bluetooth (BT-570C) and I'm currently converting it to WLAN (ESP07S) and ext. power supply. Then I can see from the house if it doesn't switch off and generate an alarm if that occurs. Unfortunately, errors that only appear sporadically are extremely difficult to track down. So I hope that this way I can act and search in time when the error occurs...

  13. #13
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    I had a weird problem with my battery randomly draining overnight. It was the alarm sensor under the hood that was bad. Just disconnect and try, open circuit is read as hood closed.

  14. #14
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    ... ohhh, good hint! Nobody think about the alarm- thingy ...

  15. #15
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    I had longlasting battery drain problems also. Until I found out that webasto unit was in short circuit and after removing it completely from the car and installing a new battery (old one was constantly jumpstarted and tester finally said that needs replacing) I finally got rid the of the problem. After that, even after a week (longest i've tried) still goes from first start.

  16. #16
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    Quote Originally Posted by kallekula View Post
    I had a weird problem with my battery randomly draining overnight. It was the alarm sensor under the hood that was bad. Just disconnect and try, open circuit is read as hood closed.
    I had this same problem as well, and was going to mention it....(mount on microfilter box was cracked allowing the whole switch (not just the plunger...) to be pushed down when the hood closed.

    One time I found that something had gotten spilled on the seat memory buttons. One of the position buttons was sticking. It didn't look that way at first but upon actual testing, it was activating a request to move the seat to P1.

    Hood switch was found by luck, seat memory switch was found by fault tracing across all fuses to see which item continued to consuming power.

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