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Thread: 850i Parasitic Leak causes dead battery

  1. #1
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    850i Parasitic Leak causes dead battery

    Hey
    I was trouble shooting my dads 1991 850I as his batteries would be flat after a few days of sitting in the garage. Last night I did a parasitic leak test and found that there was a constant draw of 0.43A. I had isolated it down to fuses 33 as when I removed that fuse the draw went down to 0.21A. and fuse 43 as when that one was removed it was 0.04A of draw. When both fuses were removed together there was zero amps of draw. My question is this what are the weak electronics on 33 and 43 that could be causing me grief. I know that if 43 is removed and the battery is reconnected I have no interior lights, the window does not lower when you open the door, and the power locks do not work.
    Please let me know if you have any suggestions,
    Thanks

  2. #2
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    Just wondering... How long did you wait before pulling the fuses? It's not until 16 minutes after the last activity the E31 enters sleep mode. In sleep mode the current draw should be around 50 mA. Before entering sleep mode a current draw of approximately 500 mA is normal.

  3. #3
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    Hi revtor
    I had the car sit for over an hour to make sure it was in sleep mode. The manual says that anything over 50mA is not acceptable. My draw of 430 mA is way too much and he has 2 1000A batteries in the trunk and you leave the car for a weekend and they are flat. We have a 1990 with 2 750A batteries and that thing can sit for over a month and still have enough juice to start up no problem.

  4. #4
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    I always find it strange that our batteries tend to be depleted after less than 2 weeks of sitting. Typical car batteries have about 45 Ah, and we have two for a total of ~90Ah. @ 0.05A draw we should have enough for them to sit for months, even with the max typical discharge rate of 20%/month.

    Or, perhaps a lot of us need to replace our batteries because it seems a very common fault in our cars

    Edit: or a lot of us have this abnormally high amperage draw problem..... I'll have to test mine because it is quite annoying
    Last edited by Hobz; 08-25-2010 at 11:16 AM.

  5. #5
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    It's not out cars, as my 8 series is not my daily driver, and she's sat for two weeks before never being touched and starts flawlessly. This however I know does not help the OP's issue.

  6. #6
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    Winks: Good to see someone actually read the manual .

    If you open the trunk (trunk lights go on), and wait 16 minutes. Do the trunk lights go out?

    Suspicious drains on fuse 33 and 43 hint towards the consumer cut-out circuit (relays K72 and K73 in the rear power distribuution box), driven by the A5 Relay Module (RM) and controlled by the A1 General Module (GM). Especially the latter is known for failures due to aging capacitors, although the car usually develops random behavior when the capacitors are bad. There's a lot of information in the archives about this issue.

    Hobz: The E31 has 2 x 65 Ah (130 Ah) stock and some fit even larger batteries. But even with the default 2 x 65 Ah batteries you should have no issues starting the car after being parked for only 2 weeks... The batteries should last a lot longer than that.

  7. #7
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    Well I always check the manuals... the manual actually states that the plunger on the trunk lid needs to be depressed to shut off the lights. It was a two man operation, I held the meter and the plunger and the old man pulled the fuses.

    Now you were saying that there is lots of info in the archives revtor, where can I find these. I have not gone as far as testing the relays but tonight I may have to test the ones you suggest. The car still runs and drives fine for now, just as long as it does not sit too long. Its frustrating to come back after a weekend away to find that the car battery is dead.

  8. #8
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    Quote Originally Posted by Winks View Post
    the manual actually states that the plunger on the trunk lid needs to be depressed to shut off the lights. It was a two man operation, I held the meter and the plunger and the old man pulled the fuses.
    The trunk lights should go out 16 minutes after the last activity (eg. open the trunk and wait 16 minutes). It's important to test this as it gives an indication of whether or not the consumer cut-out circuit works.

    The "archives" is just what comes up after using the forum search. A good topic containing a useful information about the capacitor issue of the General Module is general module success!.

  9. #9
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    Interesting about the trunk. I will try that, because my hand was getting tired pressing in the plunger.

  10. #10
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    Here is more information on current drain, although it is for the E38 it is still relevant for the E31. As Revtor says, the 16-minute wait is imperative. On the E38 the boot-lock can be fooled by sticking a screwdriver in the catch, this switches off the boot light. On the E31 you just have to wait 16 minutes with the meter in-circuit until the boot light goes out.

    Any measurement made before 16 minutes has elapsed is irrelevant. The battery voltage has to be good for these tests (12.6V), if the voltage drops too far the closed-current systems will fail to operate. The E31 has two batteries, it is much easier to disconnect one battery completely and then connect the meter between the -ve post of the remaining battery and the chassis.....and then wait 16 minutes.

    Most relevant to the E31 in this write-up is the section on battery condition:

    http://www.meeknet.co.uk/e38/E38_Battery_Drain.htm
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  11. #11
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    I tried again tonight to do a leak test but this time I left the trunk open for 16 min and the trunk lights never went out. I had waited over an hour and the lights remained on. Could this be caused by the faulty General module.
    Thanks

  12. #12
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    Just what I expected: the consumer cut-out is inactive. The A1 General Module (GM) is one of the suspects, but first have a closer look at relay K72 - it may be sticky. Pull K72 (rear power distribution box - refer to page 0670.0-02 of the 1991 Electrical Troubleshooting Manual) and measure resistance between pins 30 and 87a. There should be no connection - if there is, the relay is sticky.

    If the relay isn't sticky don't re-insert it yet and once again wait somewhat over 16 minutes (there is no point in waiting like an hour - the clock is quite accurate). Then measure the voltage over pins 4 and 8 of the socket where K72 was seated in. If you measure 12 V, the A5 Relay Module (RM) still powers the relay (which is obviously not correct).

    If you measure 12 V, either the RM or the GM are faulty. You can't measure/trace the communication between GM and RM with simple hobby tools (it's a digital bus), so pin pointing the problem to one of both is difficult unless there is other strange behavior that can be attributed only to one of both. But the GM has a much higher failure rate than the RM. Like I wrote earlier, the GM is notorious for failures due to aging capacitors. If you are not shy of using a soldering iron (or preferably a temperature controlled soldering station) you can fix the GM for a cost of a few dollars worth in new capacitors. The only thing is the failing capacitors in the GM usually show themselves in other strange behavior (eg. the power windows or wipers no longer working properly), so don't rule out the RM yet...

  13. #13
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    Thank you for your assistance
    I have had the car for a year and there has not been any other problems
    I did a close check of the rear fuse panel and I note a few inconsistencies when compared to the chart, namely:
    1) the fuse slot of fuse #35 should be empty but there is a 15 Amp fuse in place
    2) the fuse slot of fuse #41 should have a 30 Amp fuse, but is empty
    3) above the fuses 34 to 37, there is an empty slot (?relay slot) and I do not know if this should be empty or have an insert
    Thanks again for your help

    So I tested the relay k72 which was fine and not sticky. I did still have 11.68V running through pins 4 and 8 after 16 min. Called the dealer for a price check on the general module and relay module out of curiosity and found the general to be about $780 and the relay to be just over $500. These parts are not cheap.
    Last edited by Winks; 08-27-2010 at 03:42 PM. Reason: Automerged Doublepost

  14. #14
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    Quote Originally Posted by Winks View Post
    1) the fuse slot of fuse #35 should be empty but there is a 15 Amp fuse in place
    Fuse F35 is not used, so consider it a spare fuse. The Electrical Troubleshooting Manual (ETM) for later years actually shows F35 as an unused 15 A fuse.

    2) the fuse slot of fuse #41 should have a 30 Amp fuse, but is empty
    Fuse F41 is for the rear window defogger. Perhaps the previous owner experienced problems with it and removed the fuse?

    3) above the fuses 34 to 37, there is an empty slot (?relay slot) and I do not know if this should be empty or have an insert
    According to the 1991 ETM that's where the K15 (central locking) electric power protection relay should go. How many relays do you have in the rear power distribution box and does the central locking work?

    Called the dealer for a price check on the general module and relay module out of curiosity and found the general to be about $780 and the relay to be just over $500. These parts are not cheap.
    In case of the General Module, don't buy new. In almost every case it's the dreaded capacitor issue that causes all problems. Fix it yourself for a few dollars, have it fixed by someone else, or go with a refurbished module. Don't buy a used non-refurbished module as it will very likely suffer from the aging capacitors as well. For the Relay Module it doesn't really matter whether you buy new or used. Perhaps you can work out a deal with one of the breakers on this forum to buy a General Module and/or Relay Module with the option to return and refund it if yours turns out to be ok?

  15. #15
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    I had a leak in my Biturbo,, and we took all fuse out ,, and finally when we checked the rear fusebox ,, under the left seat rear,, it was fuse nr 42 ,,
    and that fuse is for the drivers seat ,, it was 350 milliamper and dropped to 50 ,, ,, and that is ok,,

    but i have to take the seat out and find the problem were the leak is

    the battery lasted max 4 days
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  16. #16
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    Hi Revtor I am only missing that one relay k15 in the rear pannel. I am not so worried about the defog as that car will never see winter, no has it ever. Do you know the purpose of the k15 central locking power protection relay?

  17. #17
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    K15 and K30 are used as electronic fuses. Without those the following functionality will not work:

    • K15: driver's power window, sunroof, and central locking
    • K30: passenger's power window

    If you don't have issues with this I can only imagine K15 is in a different location than indicated in the ETM. Perhaps this is an error in the 1991/1992 ETM because in later years K15 moved from below K30 to the right of K30. I don't know... You may want to compare your relay layout with a car of approximately the same manufacturing date.

  18. #18
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    Hmm.... I have the same thing.
    I replaced my batteries last year with two new 76A batteries.
    Car is still drained after less than two weeks.

    When I bought the car It could sit for 4 weeks and still start.
    Installation of a new stereo system and an aftermarked alarm also made no impact.

    When I got the GPS tracker installed the car is dead after 1,5 week.
    The tracker has a battery that delivers 500mA, so I guess the nominal consumption is a bit less.
    The tracker has it's own battery so I really don't understand why this should be the cause.

    Still, if the car pulled 300mA, It would take 21 days to drain both my 76A batteries.
    It the time it takes my car to drain the batteries it need to pull 600mA continiously.
    -Egil (my name)

    2012 ///M550xd touring
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  19. #19
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    Quote Originally Posted by Noggie View Post
    Still, if the car pulled 300mA, It would take 21 days to drain both my 76A batteries. It the time it takes my car to drain the batteries it need to pull 600mA continiously.
    It would take 21 days to drain the batteries completely dead. Of course your car wouldn't crank anymore long before that...

    Anyway, if I understand you correctly, the problem first showed after installing the GPS tracker. In that case the cause seems quite clear to me. What is the current draw or power consumption of the GPS tracker according to its documentation or technical specifications? It would be interesting to measure its current draw...

  20. #20
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    Hi Revtor
    Interesting....We just pulled the 1990 from storage and it too was missing the k15 in that location. Now both cars have similar history as they both followed the same path of Germany, Japan, then to Canada. I am not sure if there is slight change in the models built for different countries may have something to do with the location of k15. I am under the impression that there is a difference in some of the electronics for the US market that are different then that of the Europe market.

  21. #21
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    Quote Originally Posted by revtor View Post
    It would take 21 days to drain the batteries completely dead. Of course your car wouldn't crank anymore long before that...

    Anyway, if I understand you correctly, the problem first showed after installing the GPS tracker. In that case the cause seems quite clear to me. What is the current draw or power consumption of the GPS tracker according to its documentation or technical specifications? It would be interesting to measure its current draw...

    My car is DEAD.... as the remote lock wont open, and the dashboard lights don't even come on after 14 days.

    I too think the GPS tracker is part of the reason, if it was pulling 500mA it should take 12 days to drain both batteries.
    However I do not believe that it pulls that much, the backup battery is 500mA on the GPS tracker.
    If it was supposed to last 10 days it would pull 50mA.
    This is a simple receiver and should not need any power unless activated.
    If this was to last 20 days without a power source that is 25mA.
    Which mean that it should take 253 days to drain my batteries.
    Add inn 50mA from the car itself and it should take about 83 days.... or almost 3 months to drain the batteries.
    -Egil (my name)

    2012 ///M550xd touring
    1990 850Ia Hartge Supercharged.
    2004 M3 (sold)


  22. #22
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    I too had the battery drain on my previous 1997 840ci. It would never go into sleep mode. I kept the car on a battery tender while not driving and it would hold a charge. As the batteries got older it started to not hold charge. I had my independent track as far as he could with no luck. Finally took to a dealer and it took them some time to figure out as well and in the end it was the GM. I negotiated the cost with them and the new unit solved the problem.
    Good luck
    Dan

  23. #23
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    Noggie: It's possible you have several parasitic drains, but without measuring the actual current(s) this is all just guessing and impossible to diagnose ...

  24. #24
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    A few things that made a difference on the car being able to start after sitting for 3 weeks was the removal of the phone electronics, new alternator, and fresh batteries. (I also put a battery tender on the car for extended times)

    The alternator and batteries are obvious electrical upgrades, but the phone removal made a difference. The previous owner "removed" phone by cutting the cable in the armrest. After I unplugged the phone electronics from the wiring harness (thanks Mark Fling for directing me) it seemed that the electrical gremlins left with the phone as cutting the cable may have created a small short. The phone connection on the wiring harness is a 4 prong connector that is located at the top of the rear, driver side wheel well in the trunk.

    My next electrical project is to replace the main cable from the alternator to the battery post under the hood.

    Hope this helps others.
    Regards,

    Brian
    Cave Creek, AZ

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    The phone module not sleeping gets a few E38s as well......

    Worth unplugging.
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