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Discussion Starter · #1 ·
Hi all,
I've read through every post on battery drains here and have to add my own and hope someone can help!

I have a 2000 BMW 528i which I bought off my mechanic when I was trying to get my old car serviced and it was too dead to repair. He's on active duty in the Armed Forces and drives to and from Kingston, Ont. to Montreal, Que. (about 300KM) every week, but not much driving other than the highway every week. He's had the car for 2 years and the last 5 months or so have an intermittent parasitic type draw on the car - he's replaced all the standard items that could cause that on the BMW forums, were FSU and other units to replace suggestions.

I started to check the amp draw with a multimeter in series off the negative battery terminal post and negative battery cable clamp - it was showing a 300+ milliamp draw and the car would dies in 3-4 hours of being left off, and the voltage would drop from 12.6v before going to bed, to a 8.4v by the next morning. While pulling fuses - I found the one in the dashboard that regulate the AC and heated washer jets. After pulling it, the miltimeter showed 20 milliamp draw.

So I thought yeah! problem and mystery drain is gone! I replaced the battery a few days ago with a brand new one to make sure all is well (the old one was recharged and boosted so many times it stopped holding a charge - even though I was able to confirm there was no more parasitic draw - so replaced) New battery on, I did another parasitic draw test and again - 20 milliamps, or perfectly in line with standard specs.

2 crazy things...1. even though there is no obvious draw = the brand new battery went down from 12.6v to 12.4 a few hours later, to 12.2 at night and then 11.8v this morning. Still turned over no problem first try, no cranking needed. And registered 13.6-13.9 on the multimeter with the car running. So with a new battery and no parasitic draw, the car will still drain juice somehow.

2. now the interior heating wont work at all - all the buttons don't work/light up - I replaced the fuse and no luck. So I have no draw, no interior heating or defrost buttons work, etc. and with a brand new battery, it still drains down somehow...winter is coming and I'm pulling my hair out for 2 months now...
 

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Scenario 1. You're aligned with the rest of us, it's normal

Scenario 2. What did you do with the AC and washer jet fuse you pulled?. Did you fix the problem with this circuit?
 

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Discussion Starter · #3 ·
Hi 16valex,

thanks for getting back to me!

I've since put Fuse 9 back in and now have the AC and heater working. I'm doing a battery drain test as we speak and will know if the amp draw is more than 20 milliamps like before or if the Fuse 9 is the culprit. Should know and post some results in 10 mins.

I am happy to join the community, but was hoping not to have to live with this...I'm keen on finding the cause of the mysterious drain - since it's not showing up on the multimeter - my next thought was the alternator has a bad diode and is sucking juice back from the battery. Do we have some tests we can do/
 

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Discussion Starter · #4 ·
update - the draw test is over. with the fuse 9 back in, it reads 0.02 amp draw after 20 mins for it to fall asleep. So the fuse 9 was pulled a week ago in trying to find the draw and it WAS the cause of the draw back then (taking the multimeter from 150 milliamps to 20 milliamps once it was pulled. I put it back in today, get my AC and heater back, and it's now reading the same 20 milliamp draw...see the frustration??!!

So it doesn't look like a bad fuse now...and the car still drains the battery after a few hours. going to pull the alternator cable out now and test the battery voltage before and a few hours later to see if the draw is there.
update to follow...
 

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Yeah! The FSU is a known issue with this car. Don't bother wasting your time with alternator and battery yet, go right to the FSU and pull the connector off of it and see what kind of current draw you get.

BTW, the FSU is located on the front passenger side corner of console and firewall.
 

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...he's replaced all the standard items that could cause that on the BMW forums, were FSU and other units to replace suggestions.
Even though the previous owner may have replaced the FSU, it could still be the problem, particularly if he replaced it with a cheap eBay version, which have been notoriously unreliable. I forget the brand names of the two more reliable FSU's, but I think one was Valeo. If it turns out you have one of the cheapie FSU's, check the "very best links" sticky for FSU recommendations.
 

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Discussion Starter · #8 ·
I wish it was a bad FSU - my mechanic only buys OEM parts for this car, as he's babied it for the last 2 years - fixed anything wrong, upgraded the front struts to the 540 models specs, etc., all from Germany if possible. The FSU was only replaced 2 months before I got the car off him. I took the alternator power red cable off and left it alone for an hour - no change in voltage - was 12.2v and remained the same.

what do you guys recommend? the fuse 9 is back in and heater works great, and there is no amp draw from there now...so 20 milliamps is still the 16 minute shut-down voltage. and yet if the neg. cable is tightened back on - she'll start to drain, within 4-5 hours, no start, and dead by the next morning.:dunno:
 

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Was it the older style fsu that is big or the newer one that is much smaller. The smaller fsu's are the updated and better working fsu's
 

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Discussion Starter · #10 ·
That I'd have to check with him...which is tricky as he has a very pregnant wife about to deliver so he's up there for the next month and a half or so - which leaves me friends that are mechanics but don't have a shop/lift, etc.

Would the newer FSU, or even the older one for that matter, show a draw if defective? because I still have only 20 milliamps being drained.
 

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Would the newer FSU, or even the older one for that matter, show a draw if defective? because I still have only 20 milliamps being drained.
That's a good question. I'd search the forum for "FSU parasitic drain" to see what others have found. By the way, the newer FSU has more slender pins for the heat sink, vs. the coarser look of the older style. I'm sure you'll find comparison photos.
 

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That I'd have to check with him...which is tricky as he has a very pregnant wife about to deliver so he's up there for the next month and a half or so - which leaves me friends that are mechanics but don't have a shop/lift, etc.

Would the newer FSU, or even the older one for that matter, show a draw if defective? because I still have only 20 milliamps being drained.
20 miliamps should be fine.
 

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Discussion Starter · #13 ·
Somebody help me understand what's going on!
1. good battery, starter, alternator
2. 20 milliamp draw after 20 mins off and armed
3. fuse 9 was causing a 300 milliamp draw, removed and draw went down to 20 milliamp, after a week, put back in, and now no excessive draw for heater/AC - again, only 20 milliamps draw when sleeping - so it went away by itself??? Or is that the consensus on the board = check the FSU again, and that might be causing this?
4. since it was draining itself all day, how the hell did it recharge itself since 3 trips this afternoon?
5. I almost want to leave it armed and battery plugged in all night to see if it drains, but then we'll still be stuck trying to figure out HOW it drains as the standard multimeter test shows us on a cursory 20 Milliamp draw.
 

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Well it's pretty easy to remove on your own. Here's a good youtube video showing how it's done.

https://www.youtube.com/watch?v=rB1XMzVtdno

Here is a picture showing the difference between the two FSU's


If I remember correctly, you can take it out, and if the FSU is the problem you will have no more drain. I remember doing this to solve my problem until the part came in the mail. You will not have a heater as long as this is pulled out.
 

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3. fuse 9 was causing a 300 milliamp draw, removed and draw went down to 20 milliamp, after a week, put back in, and now no excessive draw for heater/AC - again, only 20 milliamps draw when sleeping - so it went away by itself??? Or is that the consensus on the board = check the FSU again, and that might be causing this?
There's a possibility that it could be the FSU's intermittent. If it's intermittent it will be back.

4. since it was draining itself all day, how the hell did it recharge itself since 3 trips this afternoon?
at 20 milli amps draw? I call that's normal, and that is why you were able to start the car all day.
 

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You know, there is one other possibility. There's a little fan behind the central air vents in the dashboard that runs semi-independently, sampling the cabin air temperature. I think I recall it running amok and causing a problem something like yours. If I get a chance, I'll try to find that thread, but you might search for it as well.
 

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Discussion Starter · #17 ·
thanks for all the input guys!

I'm going to leave it armed and locked all night - see what the voltage says tomorrow morning, when there'll be enough daylight to see what I'm doing and try and remove the FSU.

Crossing fingers...update to follow!
 

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See also these threads, found by typing /drain f3 in the bestlinks ...
- How to test a BMW battery & alternator (1) & the most often recommended diagnostic procedure to test for overnight parasitic battery drain (1) & one user's attempt to locate, describe, and photograph all fuses and relays in the BMW E39 with a picture of every fuse & relay (1) & how to choose a good aftermarket battery (1) and a simple battery replacement DIY (1) & Cn90's explanation of where to get alternator rebuild parts (1) & how to troubleshoot a bad FSU final stage unit (1) and how to build a test jig for your FSR final stage resistor (1) & how to repair solder cracks in your blower motor resistor (1) & how to replace your HVAC blower motor control (1) (E46) & what FSU is the right one to buy based on user experiences (1)
 

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Discussion Starter · #19 ·
sorry for the delay - car read 11.7 volts this morning. [email protected]#$%^&*(!!! then I recharged it, did the amp draw test (still 20 milliamp draw, no more), and let the wife have it for errands for the whole day, so no chance for the FSU check until tomorrow.

BlueBee thanks for your post! I've been reading them all day since I have no car to play with!loL!

could we look at other options besides the FSU though? I know my mechanic/past owner - he loved this car, had the $$$ to keep it OEM, the skills and garage to fix and upgrade it - and was working on this electrical gremlin for a few months when my then car blew up and I kinda forced him to sell me his car, on the spot, that day. So besides the FSU which he replaced and took every fricken light bulb outta the truck, hood, etc. searching for that gremlin - we got squat. It doesn't make sense to me that a car that was drawing 300 milliamps of power before, has Fuse 9 removed for a week, has the draw go down to 20 milliamp and then the fuse put back, the 20 milliamp stays the same, but the car still drains itself down overnight.

Someone with super logic needs to chime in as it's blowin' my brain fuses...one by one.
 

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FSUs can be bad right out of the box. They can also fail prematurely, and we have seen it many times. Please don't ignore the obvious. They are a troublesome area of the car. I would highly recommend you buy one from a BMW dealer...but get online, as prices are better there. The ones sold (even by the same oem manufacturer) from online independent parts houses, do not seem to have the same reliability as the factory BMW part.

I realize it could be something else, and wasting $125 on a part you may not need, but I hate to see you trying to chase down something that in all likelihood is the FSU (again).
It is a 'crap shoot", but I give it a greater than 50% chance it is the FSU.
 
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