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How to diagnose what's wrong with a battery that goes dead once a month?

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Discussion starter · #21 ·
dannyc9997 said:
The blower simply will not work.
Click to expand...
Until now, I never thought of this as a diagnostic procedure, but, it seems pretty simple.

1. Car dies periodically (and blower has wierdities at the same time)
2. Unplug FSU ...
3. If intermittent battery death stops, then you've pinpointed the problem
4. Replace FSU

I should have done this looooooong ago!
 
#22 ·
bluebee said:
Until now, I never thought of this as a diagnostic procedure, but, it seems pretty simple.

1. Car dies periodically (and blower has wierdities at the same time)
2. Unplug FSU ...
3. If intermittent battery death stops, then you've pinpointed the problem
4. Replace FSU

I should have done this looooooong ago!
Click to expand...
Give it a try, hopefully thats your issue.

The info for how to measure drain is in post #2 in this link, also other good info in the thread here...

http://forums.bimmerforums.com/forum/showthread.php?t=1079602
 
#23 ·
bluebee said:
This is a very interesting concept. Are you saying that if we remove the FSU, that the car will still work?

I hadn't thought of that. I suspect all that will fail is the interior blower (and maybe not even that because the high setting isn't regulated by the FSU according to what I read). So, maybe without an FSU, the fan would just blow 100% (or 0%?) all the time?

What happens to an E39 that has no FSU connected to it?
Click to expand...
Effectively nothing except no interior fan function, which shouldn't be too much of an issue in CA. On the other hand, not having a heater/defroster fan here in NE in Jan can be a major issue! Others have done this and their blowers become non-functional but their battery issues disappear. This indicates the cause of the drain is the FSU. If your drain continues after FSU removal, the cause is something else. A pretty simple approach to trouble shooting and diagnosing battery drain issues with no ill side effects.
 
Discussion starter · #24 · (Edited)
I replaced my $75 FSU hoping that was the cause of the monthly battery drain

Fudman said:
Others have (removed the FSU) and their blowers become non-functional but their battery issues disappear. This indicates the cause of the drain is the FSU. .
Click to expand...
OMG. It was not easy to remove that FSU from my 2002 E39! It was very difficult to get the two clips to release and I ended up breaking one of the clips while you guys were watching the Superbowl today.

The good news is I have the new FSU in and I don't hear anything running when I shut off the E39.

Time will tell if that was the reason for the monthly dead battery after sitting overnight or during the work day.

For diagnostic purposes, I took old/new resistor measurements which I'll post to the FSU thread.
If everyone with the dead-battery problem does this, maybe we'll notice a diagnostic pattern to the measurements?
And, it will be interesting to take the old FSU apart to see what's inside.

I'll let you know if the battery still dies but I hope it was the FSU.
Image
 

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Discussion starter · #25 ·
#27 ·
Cany anyone list the most common things to drain a battery in 39s? Cd changer, fsu, _____,____?

This may be helpful to some, infcluding my self
 
#28 ·
Five month old battery died yesterday. Had AAA test it, and they found the battery was draining even with everything shut off.

E39s seem to have the same common problems. So far, I've had a non-opening trunk, inconsistent A/C fan speed, and a broken CD changer - all of which are potential battery drainers.

I've fixed the trunk problem (broken wires leading into trunklid), and the CD changer hasn't worked the past 4 years or so, so I'm guessing it's the FSU. Guess I'll bring the car to the indy mechanic tomorrow again....
 
Discussion starter · #29 ·
emPoWaH said:
they found the battery was draining even with everything shut off.
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You seem to have the same problems I had ... (except the CD changer which I don't have since I only have the single Business CD) ... but I do agree ... E39 problems seem to be relatively common ...

The FSU isn't all that bad to replace ... it's 50:50. Either you will replace it so quickly you'll wonder what all the fuss is about; or, you'll be cursing the evil ears on the FSU connector like some of the rest of us (me included).

Of course, I broke off the evil ears ... and then my FSU came right out ... but I don't recommend such draconian satisfactions ... :)

Bluebee
Image
 
#30 ·
bluebee said:
You seem to have the same problems I had ... (except the CD changer which I don't have since I only have the single Business CD) ... but I do agree ... E39 problems seem to be relatively common ...

The FSU isn't all that bad to replace ... it's 50:50. Either you will replace it so quickly you'll wonder what all the fuss is about; or, you'll be cursing the evil ears on the FSU connector like some of the rest of us (me included).

Of course, I broke off the evil ears ... and then my FSU came right out ... but I don't recommend such draconian satisfactions ... :)

Bluebee
Click to expand...
Since it's my mother's car, and she doesn't want to be stranded again, she ended taking it to a local indy shop (South Bay Independent BMW) today. The FSU unit was $110+tax and labor was $90.

Pelican Parts has it online for $60 shipped; the local dealer wants $158 for the same part. I suppose I could have DIY'ed and saved $150, but that's the price you pay for convenience and assurance. It's still way less than a monthly lease payment...
 
Discussion starter · #31 ·
emPoWaH said:
I suppose I could have DIY'ed and saved $150, but that's the price you pay for convenience and assurance.
Click to expand...
Always a battle between getting it done and doing it yourself (with limited time, limited tools, and limited experience).

Without these boys on Bimmerfest, I'd never have attempted half of what I've done so far ... and certainly not what I must contemplate moving forward.

So, kudos to you for getting it done. Far better to pay the $150 and not have a battery go dead on you than to never do it at all!

Bluebee
 
Discussion starter · #33 ·
bluebee said:
Long term progress report ... It has been two years since the FSU was replaced and the battery hasn't died since!
Click to expand...
In the past two years, we've learned to stay away from the GKR FSUs (which my original FSU was) in favor of the Sitronic/Bosch for the E39.

If you're interested in the details, xref is here.
FSU (aks FSR) fan blower speed resistor autopsy and wiring diagrams (1) (2) (3) (4) ... (1) (2) (3) (4)

Image
 

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Discussion starter · #34 ·
Just to update this thread, since I often refer others with dead battery overnight symptoms to it, this seems to be a reasonable diagnosis:

- If your battery goes dead overnight (intermittently)
--> Then test your battery drain (1) (2) & test your alternator output (1)

- If the drain and alternator are good but the battery still dies overnight
- Then feel the FSU to see if it's hot a few hours after shutting the car down
--> If the FSU is hot, then unplug the FSU & order a new FSU

- If the FSU wasn't hot yet the battery is still dying, then unclip the FSU
--> If the problem goes away while unclipped, then order a new FSU.
Note: Only order the FSU brand recommended in this thread!

Note: You may also note oddities in the fan blower operation; but then again, you might not as it seems to often be intermittent.
 
Discussion starter · #35 ·
Discussion starter · #36 ·
Discussion starter · #37 ·
#38 ·
I had serious battery drain. First I thought my old battery died so I replaced it. After 4 days, that battery was dying, I had to charge it every other day. Finally after 2 weeks that battery crapped out and they replaced it under warrenty - dead cell. Tried all the FSU tests, FSU seemed ok. Began testing for parasitic drain, when I found the 'hood open' limit switch unplugged. I had done brake work last month, checked the brake fluid, and forgot to plug the limit switch back in. That was the source of the drain.

Sometimes I am my own worst enemy.

Jerry
 
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