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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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Old 12-03-2007, 01:19 PM
manminder singh manminder singh is offline
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Join Date: Oct 2007
Posts: 43
Mein Auto: 525 DIESEL 2000
Battery keeps going flat

Hi I am having a problem with my 5 series bmw 1999.
The battery keeps going flat and I have tried a new battery, disconnecting the cd changer and
have checked all lights go off when the car is parked. I now have to diconnect the battery when the car is parked to stop it from draining.
I have been told to pull the heater blower fuse (made no difference) the battery was completely dead.
This have been happening for a few weeks now. I have to book it in for a diagonistic check next week at the dealer 120+vat per hour (1 hour minium and could be more) just for them to tell me what is causing the drainage to the battery. (not to fix it)
If anyone has any idea what might be causing the battery drainage please let me know and save me a bob or two.
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Old 12-03-2007, 01:41 PM
rjjarvis rjjarvis is offline
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Location: Mclean, VA
Join Date: Sep 2004
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Mein Auto: 2001 E39 540i6 Sport
Addressing the battery drain


My first thought is that maybe your battery is not being charged properly because the alternator is faulty or because the "brushes" on the voltage regulator or the voltage regulator itself needs to be replaced.

In this scenario, you'd recharge or replace your battery, the car might run reasonably normally, but when you turn it off the battery is dead because it hasn't been charging while the car is running.

If your 99 is like my 97, it has a Bosch alternator with a small voltage regulator that fits into the alternator. Assuming the voltage regulator is the problem, it's easily and cheaply replaced on a DIY basis. But there might be additional symptoms, like your headlights not being fully bright, if the V.R. is the problem.

If the charging system itself is not at fault, it is some sort of "parasitic" drain. These can be fairly obscure, but you can find them by systematically eliminating fuses. There's a great article that addresses your problem for SAABS at the following URL: http://www.swedishwrench.com/battery.htm

Although your 5 series is, IMHO, infinitely better than any SAAB ever manufactured, the principles are the same. All you need is a suitable ammeter (part of a handheld multimeter) and a little patience.

Good luck, and let me know how you do.
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Old 12-03-2007, 01:54 PM
rjjarvis rjjarvis is offline
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Location: Mclean, VA
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Mein Auto: 2001 E39 540i6 Sport
Additional input on battery drain

Here's another good article that points out you can do the parasitic testing without an ammeter, just using a 12v bulb with two leads. If you don't have a suitable ammeter, this would be a very cheap and simple way to do try to locate the problem. Considering that the battery is in the trunk, however, you are probably going to have to have another person watch the bulb while you pull and replace fuses one at a time.

Oh, one more thing. The stuff in the SAAB article about the alternator is pretty applicable to the BMW because they both use the Robert Bosch alternator (at least in the US), and the voltage regulator looks the same.

If you suspect it is the charging system at fault, I would certainly start with Occam's Razor, viz., taking the voltage regulator off (it has two screws, but be careful because the brushes are spring loaded and it could pop out and drop into the engine compartment). Then you can carry your part to your local dealer or other parts place (chances are an import parts place would give you a SIZEABLE discount on the voltage regulator) and compare the length of the "brushes" on your unit with a new one. Keep in mind that the "brushes" are two solid copper bars spring loaded into little sleeves. In any case, if the new V.R. brushes are substantially longer than yours, it might very well be that it is time to replace the V.R.

I've had to replace many V.R.s in Bosch alternators but I have never had the alternator itself fail.

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Old 12-03-2007, 01:55 PM
rjjarvis rjjarvis is offline
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Forgot to include the article

OOPS! here's the article URL I mentioned in the last post: http://www.rpc.com.au/products/batte...e/carfaq10.htm
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Old 12-04-2007, 11:56 AM
conzi_dv8 conzi_dv8 is offline
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Location: Colorado
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Mein Auto: 92' 325i Sedan
Could be your Final Stage Unit is going out. I had the same problem - what happens is your blower fan will turn on while your car is parked with out any reason. Part is about 79 bucks: PN#: 64 11 6 923 204 But first test your alternator to make sure it is charging.

Hope this helps a little.

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Old 12-08-2007, 01:53 PM
BMW-TOM BMW-TOM is offline
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Mein Auto: 523i-325i
i have the same problem on my 2000 523i,i brought a new alternator and battery didnt make any difference,still the same problems so i posted on here like you and have been told its most common to be the fsu/fsr which i have just brought off the internet auction site for 40 which is alot cheaper to try than getting ripped of by the dealer,so id try that before taking it into the garage.
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Old 12-08-2007, 07:58 PM
ebfonhome ebfonhome is offline
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most likely the final stage unit/final stage resistor. I went through three batteries over the last month and found out the hard way. Its all over these boards if you search for it.

2008 535xi (European Delivery 10/4/07), black sapphire, natural brown, light poplar, anthracite headliner, premium pkg, sport pkg, 18" wheels, cold weather pkg, logic 7, navigation, ipod, HD radio, satellite radio.
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Old 12-11-2007, 01:56 PM
manminder singh manminder singh is offline
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Join Date: Oct 2007
Posts: 43
Mein Auto: 525 DIESEL 2000
Got a new final stage resistor and thought I fit it myself since I am handy at diy. Got all the pictures on how to fit a new one from bimmerfest and bought a new stage resistor. The only thing I never stop to think was that the pictures were from LEFT hand cars and the stage resistor is under the glove box. I live in the UK and and the stage resistor is under the driver stering wheel. Spent hour trying to find it under the glove box, took everything out and then realised that I have a RIGHT hand drive car not LEFT.(what a wally). Things got worse when the tosser at the dealer gave me a wrong part and now I am stuck till tomorrow to get a replacement.
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Old 02-08-2008, 06:04 PM
unix_phr33k unix_phr33k is offline
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Mein Auto: 2002 BMW 540i
battery keeps draining

2002 BMW 540i - 117k miles

I just wanted to say that I was having a battery drain problem for nearly 3 months. I took it to my mechanic, they had it for 3 days and said they could not find anything wrong. They obviously have to warranty their work, so I got my money back. Two days later the battery was dead again, and again, and again...
I've tried replacing the battery twice, testing the charging system, pulling fuses and testing them 1 by 1, testing the alternator, and testing the battery with a volt meter every hour or so while the car was shut off. It would sometimes drain and sometimes not, but I could not narrow the problem down.

Finally, after reading through the forums here I tried replacing the FSU, Final Stage Unit. AKA, Blower Motor Resistor. Three days of driving and NO battery drain so far!

My FSU experience. Let me tell you that you really need to remove the panel underneath the glove compartment also. Unless you are a very small person, it's nearly impossible to get to in the 540i. I will have you know that while I was down underneath the dash going mentally insane trying to remove the wire from the FSU by squeezing the clips on the side of it like the walkthrough said, it wouldn't come off. I just reached in with a screwdriver and broke the clips off!! Are they really necessary? Not really. The wire is pretty snug on the FSU. Don't give up, it will come out! I promise.

I also noticed a steady flow of air blowing out from the vent directly above my face. The fan was continuing to blow even though the car was off. A very good indication that the fan blowing at an idle speed was the draining issue. Why that never came up in a test is beyond me. After replacing the FSU with the new part, low and behold the fan stopped blowing. See, tiny miracles can happen!

This may not be your issue, but if your battery keeps draining and you've tried everything, then I recommend replacing the FSU.

FSU replacement walkthrough:

I ordered the FSU from here:

FSU part #:
64 11 6 923 204

Thank you Bimmerfest for saving me from 3 months of dealing with a dying battery!!! I really appreciate it everything you guys do.
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Old 02-09-2008, 01:58 AM
Raymond919 Raymond919 is offline
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Mein Auto: 1997 BMW 528i
Manminder Singh, let us know how you made out!
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Old 02-10-2008, 09:23 AM
xaff xaff is offline
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Mein Auto: 97' 540i

Where do you get the voltage regulators for the alternator from?

Any idea where I could get those from for 540i ( i think 140Amp) ones?
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Old 02-03-2011, 06:28 AM
colls colls is offline
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Location: Warrington
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BMW Regulators

You can get these regulators supplied and or fitted from mcalternators.com . Better than paying 500 for a new one from the dealer. I got my 140 amp unit done for about 125
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Old 02-03-2011, 07:51 AM
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bluebee bluebee is offline
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Originally Posted by xaff View Post
Where do you get the voltage regulators for the alternator from?
This being a very old thread, I'll just respond to the question posed today ...

In the VERY best of E39 Links look for the alternator rebuild threads.

There's a thread by cn90 there for the Bosch alternator; and another one by aioros for the Valeo alternator.

Each one shows exactly where to get all necessary parts, including the voltage regulator (which also includes the brushes).

Last edited by bluebee; 02-03-2011 at 03:52 PM.
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Old 02-03-2011, 01:08 PM
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Flybot Flybot is offline
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Way to bring a Thread from the Dead
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