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I recently purchased a 328i. The battery will not hold a charge, despite supposedly being only six months old. The hydrometer on it shows it's good. I've taken it to Sears and had it load tested there; it tested good. I've also load tested it myself, following a procedure I found online (involving turning on highbeams for six minutes), and it also came up good, even when I tested it twice in a row without recharging it. However, if I let the car sit for a day or so, the voltage goes way down, and the motor won't crank. I've tested for shorts, and my digital tester shows only .01 amps of current flowing when the car is at rest. I understand that's well within specifications, but don't know for sure. Anyone know how much current a resting car should have flowing???? The alternator is fine, and the car charges when I drive it. It only loses power when it sits for several hours. Any ideas what could be going on?

I read elsewhere on this forum that a bad Final Stage Unit (FSU) can cause the fan to come on when the ignition is off, and thus run down the battery when the car is parked. Is there a procedure to check the unit? I don't even see the FSU mentioned in the Bently manual. I hate to start randomly replacing parts to solve a problem.

The FSU seems like a good lead. I've noticed that sometimes when I turn the ignition on, the climate control is on, with the fan speed on low, even when I've turned the climate control system off before turning off the ignition. I haven't found the fan actually running with the ignition off (as some folks have said happens with a bad FSU), but I also just noticed a low humming/buzzing sound coming from the climate control unit after I turn the ignition off. The sound is definitely coming from the dash, not the fuel injectors or something else. The pitch of the sound changes when any of the buttons on the climate control are toggled. The noise does eventually stop when the car sits long enough.

I was able to measure the current flow while everything in the car was turned off, but that noise was present, and it was about 1.5 amps for a minute or so, and then eventually dropped to .26 amps. That drain continued for a couple minutes after the ignition was turned off. I ended up breaking the connection before whatever was draining power shut down on its own.

I'll appreciate any good suggestions.
 

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Check your boot light and glovebox light are not staying on and killing the battery buddy. Common fault :)

FSU is also called the Final Stage Resistor or Hedgehog too mate
 

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i had the same exact problem. and i took mine to my local garage to have it checked out because i couldnt not find the problem for the life of me. they said the problem was two wires in the trunk were rubbing together and now its fine. the only problem is that they didnt tell me what wires they were so i cant help you there but i would just start by making sure nothing is rubbing. good luck i know how much it sucks!!
 

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Wow bro..

That is the most common problem is almost any BMW. Try the "SEARCH" function of this site.
Aloha.
 

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i had the same exact problem. and i took mine to my local garage to have it checked out because i couldnt not find the problem for the life of me. they said the problem was two wires in the trunk were rubbing together and now its fine. the only problem is that they didnt tell me what wires they were so i cant help you there but i would just start by making sure nothing is rubbing. good luck i know how much it sucks!!
Common issue with the wiring harness going from the trunk to the trunk lid gets crushed over time and it will evently cut through the wires..
 

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Thanks for help. This problem has defied logic for about two weeks. I haven't found any unusual drain on the battery that would explain its lost voltage. I checked all the usual suspects; lights on, shorts, etc. The battery passed a couple load tests, and was charging back up around 12.6 V when driven, but seems to have self destructed today. The voltage suddenly dropped after I drove the car for a half hour, and it continued to drop, even when I disconnected the negative lead. It charges a little, but stayed below 11 V, even after a 45 min drive home. With the motor running, it was charging at just under 14V, but as soon as car is shut off, voltage goes down to about 11 V, and keeps dropping until stabalizing at about 10.5V. Bit the bullet and installed a new OEM battery. Hope there's no underlying problem that I can't find.
 

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battery drain

I am also experiencing the same problem you described. I have a 1998 328is, when it's driven daily - no problems. But, if it's left sitting for about 2 days battery is dead.

I changed the battery twice already - same problem.

I read in one of the posts that there could be rubbing wires in the trunk. I'm going to check that out this weekend.

Were you able to fix your problem?

I would appreciate any help.

Thanks,
paul
 

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........I've tested for shorts, and my digital tester shows only .01 amps of current flowing when the car is at rest. I understand that's well within specifications, but don't know for sure. .
Either there's no electrical drain anomaly or you don't know how to test for shorts.

If there was a slow drain on the battery (whether it be a light, fan, or whatever) the current consumption will show on the meter if the test is performed properly.

To test if the battery is fine, disconnect the negative post from the car for a day so that there is no power to the car. Reconnect the negative post the next day to see if the condition exists. If the car starts, then for sure it isn't the battery self draining.

To test for parasitical drains, disconnect the negative post from the battery. Connect the (+) lead of an Amp meter to this ground wire and the (-) lead of the Amp meter to the battery terminal so that the meter is in series. Whatever the car is draining, you will see it in the meter.

Most meters will handle up to 10 Amps for current detection and is fused to ensure it stops dead shorts. If the fuse blows or the leads of the meter gets really warm and melts, you have a serious drain somewhere.
 

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Could a bad connection between the battery earth cable and the chassis cause the power drains or possibly an intermittent alternator problem?
 

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Could a bad connection between the battery earth cable and the chassis cause the power drains or possibly an intermittent alternator problem?
No power drains are caused by a device using power. It's not like water in a damn and a broken pipe spilling water....in electricity something has to consume it to drain, it can't just vanish.

Intermittent alternator problems won't drain it either, since the alternator doesn't run when the motor is off and that's when the drainage occurs.
 

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i'm having the same problem on my 94 325i if i let it sit overnight batt goes dead, done the amp draw test only pullin 0.02 amps, fixed broken wires in trunk,unhooked trunk and glove box lights still drains overnight.

did you ever get yours fixed? this is drivin me crazy
 

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....done the amp draw test only pullin 0.02 amps, fixed broken wires in trunk,unhooked trunk and glove box lights still drains overnight.
You did not perform the test properly if you believe your DME and other computers together are only drawing 0.02 Amps at rest.

A healthy draw, with car computers and clock, should be around 5 watts which is about 0.25 - 0.4 Amperes. 10 times what your results are.
 

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when i test voltage on mine between the pos post on the batt and the pos cable its reading 12.5 volts on the meter is this normal?

it will also read this when i unhook the cable from the distribution block on the firewall does this mean the cable is grounded out somewhere between the box and the batt
 

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when i test voltage on mine between the pos post on the batt and the pos cable its reading 12.5 volts on the meter is this normal?
yes it's normal and the voltage indicates it's a healthy battery. Read my post above to test current draw...it's a different procedure.

.... it will also read this when i unhook the cable from the distribution block on the firewall does this mean the cable is grounded out somewhere between the box and the batt
I don't know what you are trying to express here. :dunno:
 

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Could a bad connection between the battery earth cable and the chassis cause the power drains or possibly an intermittent alternator problem?
It won't cause power drains per se, but since it is a high series resistance, it can and will cause improper charging of the battery, and failure to get enough cranking current.

A poor battery connection can cause the alternator to see the battery voltage as higher than it is, but is unlikely to cause any alt failure.
 

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yes it's normal and the voltage indicates it's a healthy battery. Read my post above to test current draw...it's a different procedure.



I don't know what you are trying to express here. :dunno:
what im sayin is if i disconnect the pos cable from the batt and connect the volt meter in between the cable and batt its showing voltage between the two is this normal?

i tried the test that you described and it was only showing 0.02 amps on my meter, what should the meter be set on? i had mine set on 20m in the dca section, maybe i need a new meter.
 

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......i tried the test that you described and it was only showing 0.02 amps on my meter, what should the meter be set on? i had mine set on 20m in the dca section, maybe i need a new meter.
What should your meter be set on to observe current readings? :dunno: I don't own your meter and have never read the instruction manual for it, nor do I intend to. That's your job.

I doubt you need a new meter, just familiarize yourself with your tools first and understand how it works. Economy meters usually require you to turn the dial to some setting and plug the banana plug leads into the appropriate sockets depending on what you want to observe. The right dial setting combined with the wrong socket selection will result in incorrect readings. The wrong dial setting combined with the right socket selection will also result in incorrect readings.

I have a fairly pricey Fluke VOM, just turn it on and use, nothing to set, nothing to turn. I don't like to think about my tools and guages when I'm trouble shooting,....I already have enough to think about.
 

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So i'm browsing google for a specific topic on certain model bmw's, and I come across this post. This is directed to Mary99. NOT everyone in the world has unlimited funds to purchase a Fluke 88V (common fluke automotive meter). I would assume that you paid in the $400 dollar range for that meter, because that is what the going rate is. How do I know? I work on cars for a living, and I also do know that knowing how your tools work is one of the most important things when you are trying to troubleshoot a vehicle. When you say that you dont want to think about it, you're choosing to be stupid. Priding yourself on your ability to diagnose vehicles, your knowledge in automotive tools, and the respect you show to others who, today are not as knowledable as you are, is being a smart technician.

Also, when someone is new to the game of car repair they have no idea what any of their tools, meters, gauges, and specialty tools do. So esbslim is asking a legitimate question, to which a reply of look at the instruction manual and if you don't understand it send us the model number and maybe one of us can help him figure it out.

As far as the mysterious battery drain is concerned, testing each circuit individually is a start. the easiest and cheapest way to START narrowing it down is buying a test light. Then disconnect your negative terminal and hook the test light in-line with the negative terminal on the battery and negative battery cable. The light will light up if it is correctly done. Now, start pulling fuses one by one while observing the light. IF the light goes out then you have found your circuit with the draw; sometimes the light might not completely go out, but dim down significantly. You can perform this with a voltmeter as well (preferably the fancy meters for some). Again this is a start and will not necessarily give you a final answer on your problem.
 

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For PEMD5555, you actually mentioned a test that I was thinking of trying on my current electrical problem (separately posted here: http://www.bimmerfest.com/forums/showthread.php?p=5800058#post5800058). I have very little electrical knowledge, so if you don't mind, I have a couple questions about your suggestion.

I'm not sure what you mean by a "test light", but I do have a multimeter (Sperry SP-10A found at http://www.sperryinstruments.com/documents/products/sp-10a.pdf), but am not too knowledgeable on using it. Can I use this multimeter to test the drainage you're describing? If so, do you know what settings I'd use on the meter and how I'd connect it to the battery?

Thanks so much!
 

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Ahhh MADIME glad to help ya. Thank you for the link to your meter's instruction manual. Unfortunately your meter cannot test the range needed to pinpoint the draw. One setting on your meter is DCA 250ma which is a test for amperage, but is not a wide enough range to find a draw big enough to cause your issue. What your meter can perform is as voltage test. plug in your leads (red to the + port and black to the - port.) and then set the dial to DCV 50 which will have the appropriate range to see what voltage is getting to your battery while the car is running. Then put the red lead to the + terminal on your battery and the black lead to the - terminal on your battery. Observe on the meter what you are getting for a voltage. My general rule of thumb is seeing that the alternator is at least putting out 14volts to the battery. They say that high 13 volts (i.e. 13.7, 13.8V) is ok, but i do not like to see that. IF that is within specifications for charging then you have a draw somewhere. ALSO make sure that your battery terminals are connected properly and tight (it has happened to me in the past we all start somewhere haha).

If that checks out, go to advance or napa and pick up a test light. they range anywhere from $8 to $16. Heres a link to what they look like. http://www.amazon.com/TEST-LIGHT-CIRCUIT-TESTER-REPL/dp/B0015DMH1Q . what you do is disconnect your negative terminal and connect the test light inline with that. the test light clamp to the terminal post and the test light lead (metal rod) to the negative terminal. It will light up. The best thing to do is let the car sit for about 20 minutes so that all of your modules will power down. In terms of BMW's they love modules, and they love giving them all power and that can cause a problem. After it is hooked in line (use a friend to look at the light in the trunk). Start pulling your fuses one by one. IF the light dimms when you pull a fuse then there is a problem in that circuit. It may even turn the light completely off.

heres my example: 1999 BMW 328i E46 sedan. Customer replaced battery and is now experiencing a parasitic drain that causes the battery to die after sitting over night. Ran the test (described above) Found that pulling the climate control fuse caused the light to dimm, therefore there is a problem in the climate control circuit. Narrowed it down to a blower resistor issue. Test took me roughly two hours to perform and will bring in a couple hundred bucks in diagnostic time.
 
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