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Go Back   Bimmerfest - BMW Forums > BMW Model Discussions > 5 Series > E39 (1997 - 2003)

E39 (1997 - 2003)
The BMW 5-Series (E39 chassis) was introduced in the United States as a 1997 model year car and lasted until the 2004 when the E60 chassis was released. The United States saw several variations including the 525i, 528i, 530i and 540i. -- View the E39 Wiki

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  #1  
Old 06-21-2016, 10:14 PM
kl3vr kl3vr is offline
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Battery drain over 2amps - checked all fuses and FSU

I've got a parasitic drain issue. couple days ago, went to start the car and had no remote key entry and no power in the car. did a voltage test (battery still connected to car) and measured 0.96volts!
So I charged it up overnight (still connected to car) and measured in the morning 12.86v.
Later that day I started testing for parasitic drains with my ammeter connected in series to the negative terminal. At first I measured around 3.5amp drain (after the glove box light went out). I went through all the fuses in the glove box, noticing that fuses 5, 10, 24 and 29 caused the car to wake from sleep mode. when that happened I just waited for the light to go off again and resumed testing. By the end of the day the battery was reading 8volts

At this point I opted to have the battery tested where I bought it, thinking it suffered some kind of short. The battery was bought in January 2016, so only six months old. I havent had any problems since replacing it. They tested the battery and measured 978CCA and no battery faults. I took the battery home after testing (they charged it as part of the testing) and measured 13.0v. I left it overnight outside the car and in the morning, measured 12.86, further proving the battery didnt self discharge.

So, back to the fuses.... running through all the fuses one by one, I found with fuse 14 (possibly 15) the drain dropped from 3.5 to 2.25 amps. now it sits consistently around 2.25amps.

Somewhere along the testing, the drain dropped to 0.25amps and remained there (I wasnt able to isolate it to a fuse, it just dropped and stayed at 0.25) however it has since returned to 2.25amps and I havent been able to reproduce the 0.25amps, even after going through all the fuses again.

Next I went through the fuses in the trunk, no change. Then I unplugged the FSU, no change.

So, I"m out of ideas...

250mA would still be too high right? I read others are in the sub 50mA?

where else should I test?

The most recent work, about a week ago, was replacing the power steering pump, belts and coolant reservoir.

Is the glove box light a sure indication that the car is in sleep mode? I was using it to determine if it was safe to resume testing, perhaps the car was still awake?
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  #2  
Old 06-21-2016, 11:15 PM
edjack edjack is offline
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Easy to keep the boot open. When the lights in the boot go out, the car is asleep.

Have you disconnected the amp?

The problem of pulling and reinstalling fuses is that you may trigger wakeup, and also scramble modules.

Try this:

Finding parasitic current drain

An article in Motor magazine suggest this approach: measure the voltage drop across the fuse. It s/b zero. If you measure several (or more) millivolts, you can consider that circuit suspicious.

Some modules do not take kindly to pulling fuses, and you may encounter a lockup or damage. This approach avoids that, as well as the hassle of pulling fuses.

Also, this can identify blown fuses, where you will measure the battery voltage.

Here's a table that relates current drain to voltage drop across fuses: http://www.autonerdz.com/yabbfiles/A...crossfuses.pdf
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Last edited by edjack; 06-21-2016 at 11:18 PM.
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  #3  
Old 06-22-2016, 02:17 AM
mjayc mjayc is online now
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Mein Auto: 2001 E39 530i
Alternator? Sounds strange but I had a Lincoln LS with a faulty alternator which caused a parasitic draw and my mechanic couldn't find it till I came across a YouTube video on some guy and his Honda with a parasitic draw and he was stumped. A bad diode could cause a short and there's your draw

I swapped the alternator and the LS has been running fine since then, no longer dies after sitting. Does it apply to a Beemer? Maybe :P Try pulling off the alternator post

See the video;

Last edited by mjayc; 06-22-2016 at 02:24 AM.
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  #4  
Old 06-22-2016, 07:57 AM
rdl rdl is offline
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When the car is asleep it should draw ~25 mA ( 0.025 A ) or less.

There are several/many modules fed B+ permanently through the high amp (80 - 200 A) bolt in fuses found in the fuse block above and forward of the battery (not the "regular" fuses & relays above and slightly behind the battery) and then the fuse block under the right side front footwell. If one of those modules develops a fault it can drain the battery without any current flowing through the fuses you checked. Another possibility is a faulty alternator or starter solenoid, as mentioned above.

A first step:
1 - let the car go to sleep
2 - disconnect the heavy gauge cable (35 mm2 / ~2 AWG) running to the trunk fuse block from the +ve battery post terminal. It's attached by a small bolt to the battery +ve terminal. If more convenient, I think you can unbolt it at the fuse block instead - have a look, it will be obvious.
3 - put your ammeter between the battery post and the terminal on the disconnected 35 mm2 cable. The car will probably "wake-up" when the ammeter is connected & you'll have to wait for it to go to sleep again.

You'll then know if the ~2 amp draw is through the alternator (or starter solenoid) or through the car. If the alternator is suspect, check battery drain amps with the 35 mm2 cable disconnected. In that state, only the starter solenoid and alternator are connected to the battery. Unless there is a weak short to ground in the cable run from battery to starter - which is extremely unlikely.

If the drain is in the car's fused circuits, you'll need to start checking through fuses F100 - F106 (in the trunk) and F107 to F113 (right footwell). Once you've found the fuse with the 2A draw, you'll have to start disconnecting modules until you find the culprit.

Do you have wiring diagrams for these fuses, so that you can work out which modules each connects?
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  #5  
Old 06-22-2016, 08:29 AM
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eparayno eparayno is offline
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Maybe it's the hood alarm sensor? It can be left disconnected but folks have had battery drains and it was the culprit. It's attached to the drivers side cabin filter.
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  #6  
Old 06-23-2016, 12:54 PM
kl3vr kl3vr is offline
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thanks everyone - I'll jump on the alternator scenario today as I did have a power steering fluid leak that was dripping around the alternator for years (its fixed now - stainless hoseclamps FTW)

I'll check the hood alarm sensor as well.

and I'll find some wiring diagrams if the initial "35mm2 cable test" isnt conclusive - unless you have them handy?

thanks again!
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  #7  
Old 06-23-2016, 01:19 PM
kl3vr kl3vr is offline
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YUP isolated the parasitic drain to the thicker +POS cable. Glad to be moving in the right direction, but not happy about the potential 500$ alternator replacement. researching now if I can fix myself...
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  #8  
Old 06-23-2016, 02:22 PM
rdl rdl is offline
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If it is the alternator as it appears, the problem is almost certainly a failed diode in either the voltage regulator or in the diode plate (which rectifies the stator windings AC output into DC). I'd suggest finding a dedicated autoelectric shop for a test to determine which. Either fault can be corrected. R&Ring a voltage regulator is a DIY job if you wish to do it. Replacing diodes in the rectifier is specialized work. Either way you keep your otherwise good alternator and avoid the risk involved with a rebuilt, exchange unit.

There are many reports of most rebuilt alternators being problematic due to cheap (in every sense of the word) parts used. There are exceptions to the rule, but hard to find.

It would be worth your while looking up CNN's alternator rebuild thread to get a sense of what's involved.

EDIT:
once the parasitic draw problem is corrected, you should have your battery properly tested. A 2 amp draw shouldn't discharge a good battery in the few hours that you described. The deep discharges your battery experienced is extremely harmful to an automotive battery's life. A deep discharge battery would have fared better, but even they wouldn't like being discharge to less than 1 volt. It's likely that the CCA test you had done was performed with one of the cheap test rigs that loads the battery for only a few seconds and then uses a bunch of assumptions to extrapolate for a result. These are known to be inaccurate. And I assume the test was done by the battery vendor? Hardly an unbiased party. And sorry to say, but if they are aware of the depth of discharge cycles, the warranty is probably voided.
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Last edited by rdl; 06-23-2016 at 02:41 PM.
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