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7 Series - E38 (1995 - 2001)

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  #1  
Old 01-26-2013, 11:35 AM
crhodes435 crhodes435 is offline
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Mein Auto: 2000 740il
Battery Draw and Fail mode

Lately I have started the car and the Tracking control, brake and ABS light come on and the car goes into FAIL mode. I charge the battery and the car is back to normal. I had the battery tested and it is in good condition but had a low charge. I unlocked the diagnostics computer on the dash and am able to read the alternator is putting out 13.8 amps while running ( I also tested with a meter at the battery) . I opened the trunk and disconnected the ground cable and hooked up an amp meter and there is a 11 to 12 amp draw on the system when the car is shut off and all the doors are closed. I even tried hooking a jumper cable to the neg battery post and one to the ground cable and closing the truck and testing the draw by connecting the meter to the other end of the ground cable. I tried pulling all of the fuses and relays one at a time but nothing will make that number drop. I am open to any suggestions on what to do next. For now I am simply disconnecting the battery when the car is not in use.
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  #2  
Old 01-26-2013, 02:17 PM
setconstr setconstr is offline
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re:

My experience has been similar to yours. I am running an interstate battery I had everything checked and it all passed but still leave anything on for ten minutes and jumper cables to restart it very frustrating. My battery was 40 months old and thats about how long the last one lasted so I got a new one this week $95 as the warranty is 3 years full and 2 years partial it's all good now ..........
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  #3  
Old 01-26-2013, 04:14 PM
chrisn7 chrisn7 is offline
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What you have been attempting to do is a battery drain test. The way to do this is to open the boot (trunk), then close the latch with your ignition key to simulate the boot being closed. After connecting your ammeter, you must wait a minimum of 16 minutes for the car to go to sleep, to see what the real standby current drain is.
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  #4  
Old 01-26-2013, 04:22 PM
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BMWFatherFigure BMWFatherFigure is offline
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Is the OP confusing Volts and Amps?
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  #5  
Old 01-26-2013, 07:04 PM
crhodes435 crhodes435 is offline
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Thanks. I am charging a borrowed battery and I'm going to test that tomorrow. I will also do the drain test using the ignition key to simulate closing the trunk and I'll wait the 18 minutes for the car to go to sleep. I would not be surprised if I am confusing Volts with Amps either. Thank you for responding to my post and I'll post the solution as soon as I find out what it is. I love the car and want to keep on top of things. I just put in a new MAF 3 weeks ago. I tried a cheap one and it didn't work so I purchased an OEM one which works great. If it's the battery I'll be sure to get one that's rated for the car.
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  #6  
Old 01-27-2013, 02:33 AM
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BMWFatherFigure BMWFatherFigure is offline
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If you get a chance also check the battery cables, terminations and joints. A poor joint (volt drop) will cause all sorts of unrelated problems to appear.
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  #7  
Old 01-27-2013, 03:52 AM
chrisn7 chrisn7 is offline
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+1 on the terminals-be sure to look inside the battery post terminals-they can look perfect on the outside...
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  #8  
Old 01-27-2013, 05:23 AM
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BMWFatherFigure BMWFatherFigure is offline
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+1 on chrisn7 - found that out on the daughters Mustang yesterday!
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  #9  
Old 01-27-2013, 07:03 AM
crhodes435 crhodes435 is offline
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On a different issue. Whenever I lock the car using the key after about 5 minutes the alarm will go off. I am guessing that it's the motion sensor. Is there a motion senor in the 2000 740il and can it be adjusted for sensitivity?
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  #10  
Old 01-27-2013, 11:48 AM
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bluebee bluebee is offline
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I had whacky things happen to my cluster when my battery was just at the mid-point from being bad and good ...

- One user's experience debugging a half-dead instrument cluster (1) which, after testing the fuses (1) battery & alternator (1) thankfully turned into an alternative battery search (1) and a simple battery replacement DIY (1)

At the very least, the OP should test the charging system with redundant tests (to make sure that what he thinks is there is really there):
- DIY how to test a BMW battery & alternator
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Your job, in return, is to read the suggested threads, where the best people will always add value to those threads, either by pictures or by descriptions, so the next person with the same problem stands on your shoulders.
See also: E39 Bestlinks & How to easily find what you need
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  #11  
Old 01-27-2013, 05:18 PM
crhodes435 crhodes435 is offline
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So I was able to do the parasitic draw test thanks to the instructions I got here. There is no parasitic draw on the battery after the car goes to "sleep". I did unlock the dash panel and saw that the alternator is charging correctly at 13.8 most of the time. It drops a little at idle when I use the brakes but not below 12. I am wondering in there is something drawing too much power when the car is running and that is whats causing the issue. Last night I had to drive home about 40 miles in FAIL mode and the lights never dimmed or anything like that even at an idle. I charged the battery over night and the issue went away. But I was driving it again today around town and it happened again. If there was a circuit drawing too much during normal operation the fuse should pop so I'm not really sure where to go from here. Should the car run on just the alternator with the lights on? I started the car and disconnected the positive cable and it kept running but when I turned on the lights it died right away.
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  #12  
Old 01-27-2013, 06:46 PM
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BMWFatherFigure BMWFatherFigure is offline
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Pulling a battery terminal on a running engine will cook the alternator 80% (or more) of the time. I think you have just exchanged a bad battery problem TO a bad battery plus cooked alternator problem. Sorry.
__________________
Good - Fast - Cheap: Pick any two.
Current:
E23 735i; E32 735iL (X 2 - 1 Alpine White and 1 Glacier Blue); E34 535i; E38 735iL; R50 Cooper; R55 Cooper Clubman.
Previous:
E21 318i; E30 318i; E32 735iL; E34 535i; E38 730iL; E53 4.4i
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  #13  
Old 01-28-2013, 03:55 AM
crhodes435 crhodes435 is offline
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I'm just going to pony up for a new battery. I only pulled the positive cable off for about 5 seconds and the alternator is still running to spec. Thanks for the posts!
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