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Discussion Starter #1
hi folks

ok had to keep jump starting the car so put a new battery in and still the problem remains,the car recharges the battery after a drive so i think the alternator is ok but is there a common thing in these cars that can drain the battery? none of the lights stay on and ive been switching off the monitor etc, my car is a year 2000 m5 .
 

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Maybe the FSU.
 

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Does your beast have Navigation? If so, there are a couple of fuses in the boot (right side) that you can disconnect and see if it makes a difference.
 

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FSU = Final Stage Unit. It's a resistor pack under the dash on the passenger side used to control the HVAC blower. Easy to disconnect, and it is one of the most common sources of high current drain after the car should be asleep.

I had the local Dinan shop tech show me how the connect an ammeter to the battery to measure the sleep current after 20+ minutes of inactivity. Thay way, I could isolate the problem without waiting for the battery to be drained again. Just be sure to pull the battery ground lead after the nav unit light stops blinking (usually about a minute, but mine was taking 10 min or so to power down).

I had the same problem and tried disconnecting the FSU, but that wasn't my problem. I isolated it to the Mk 4 nav unit not powering down. Turns out the firmware had gotten corrupted. After much trial and error, I used NavCoder to force a re-load of the firmware, then had to replace a blown DVD laser head.

My thread is at:
http://www.m5board.com/vbulletin/e3...162004-mk-iv-nav-wont-power-down-fixable.html

Good luck!
 

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Pictures of FSU

The final stage unit (FSU) is accessed by removing one screw on the right side cover, just to
the left of the glove box, and then sliding it aft. Pictures below show what the original style
of FSU looks like (first photo) with the large, tapered elements. If yours looks like this, then
replace it. Remaining pics show the connector release and the tab for removing the FSU.

Regards,
Alan
 

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Discussion Starter #10
hi
ok thanks folks, if i remove the fsu what will happen to the car? do i need to replace it right away?
 

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hi
ok thanks folks, if i remove the fsu what will happen to the car? do i need to replace it right away?
The FSU (or FSR-final stage resistor) controls operation of the blower fan for the HVAC system. So, removing it means no air or heat being blown into the cabin of the car. My car had the same battery draining problem earlier this year, and the FSU was my culprit. In my case, when I turned the car off the blower fan would sometimes still continue to operate for a while. It would basically turn the fan on when the car was off, draining the battery. I recall the part being around $60-70 I believe, and it only takes 30 minutes maximum to replace it. Access to it in the E39 is relatively easy.
 

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One way to find out, turn off the car, take out the key.. pop the bonnet.. (hood) and sit and have a beer.. If during your beer you hear your fans come on a bit.. finish your beer, close the bonnet.. order an FSU, fit it and your problems are over :)

I had this problem I would put serious money on it being your FSU. If you have an older version of it just change it anyway because it's bound to fail sooner or later.

Cheers

Craig
 

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Discussion Starter #14
haha now that sounds like my kinda fault diagnosis! 2 bottles of corona should do it ;)
 

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So I replaced my FSU about a couple months ago and now I'm having issues with the battery too. The car is at the shop and will be diagnosed overnight for a drain. Does anyone think this will actually determine where a drain is coming from?

Tnx
 

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So I replaced my FSU about a couple months ago and now I'm having issues with the battery too. The car is at the shop and will be diagnosed overnight for a drain. Does anyone think this will actually determine where a drain is coming from?

Tnx

All that will do is tell them that a drain exists. They will need to monitor voltage on the battery while car is just sitting and pull various fuses to determine what is doing the draining.
 
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