Battery Drain Problem, E39

I was recently suffering from an intermittent Battery Draining problem on my 2001 E39, UK car (right hand drive).
The only symptoms were a dead battery in the morning or when returning to my car at the end of a working day. A huge inconvenience, being stranded late at night / early mornings numerous times. I first changed my battery, lasted 2 weeks then dead again. Then began pulling fuses and testing for drain, this was labour intensive at local independent garage and as the fault was intermittent fault not found, ££££ were adding up.http://www.bimmerfest.com/forums/ima...ies/cursin.gif

Long story short I changed my Final Stage Unit (FSU), even though I did not have any Heating / cooling/ fan problems, as threads on this forum had indicated this part is a major problem on the E39. This has fixed the battery drain problem completely and has ended a long period of unhappy motoring.

I bought the part for £63, not from BMW, and thanks to an excellent post from Elvis 530i http://www.bimmerfest.com/forums/sho...d.php?t=143393 I fitted the part in around 30minutes. I have attached my own photo for clarity as mine is a UK car (right hand drive). Whilst my head was in the foot-well changing the FSU I could feel the fan blowing in my ear, the key had been out of the ignition for 3 hours. So it appears the fan must have been running intermittently at low speed whilst the ignition was off and draining the battery overnight.

This website has saved me a lot of time, money and further unhappiness. Thanks to Elvis530i and Bluebee for their posts, if everyone continues to post their problems and solutions then hopefully it can help others at some point, thanks again.http://www.bimmerfest.com/forums/ima...lies/thumb.gif

Thanks for the feedback. You symptom is the third one I've read, where you encounter no blower problems, but the battery is drained.

The other two symptoms are erratic blower operation, and no blower operation, usually accompanied with battery drain.

i dont know
maybe i have the same issue
i just feel my 1 year old Interstate battery is not good as it was before
nothing dead but battery feels weak
maybe its just a winter time but i try to charge it from time to time

I bought this Final Stage Unit (FSU) and I will try to change it
Lets see

Originally Posted by champaign777

nothing dead but battery feels weak

From the VERY best of E39 Links, look up how to TEST the battery:
- DIY how to test a BMW E39 battery & alternator

I'll add your picture and commentary to the canonical FSU thread:
- FAN CONTROL GOES HAYWIRE: poorly ventilated final stage resistur/final stage unit (FSR/FSU) modules that are practically sure to go haywire due to poor heat-sink design (1) (2) (3) (4) (5) (6) (7) (8) ... Autopsy (1) (2) often causing the battery to drain overnight (1) (2) (3)

Do you have a picture of the label on your OLD FSU?

my OLD FSU is on the car
I will update this thread if i'll find something

After 3 weeks of no problems, the drain has returned. I will start a new thread on this.

I have removed the number 9 fuse which shuts off the AC / Heater & fan system to start with to see if this I can confirm this is the faulty area.