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Old 02-07-2013, 05:02 AM
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Fudman Fudman is offline
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Location: Sudbury, MA
Join Date: Apr 2007
Posts: 6,823
Mein Auto: '02 530i Sport auto
Originally Posted by bluebee View Post
(Advice is always welcome!)

I think I know what to do; so as to add value with every repair, here's my story, as it unfolds.

a) I had put in a new FSU in, oh, about three years ago (need to check) <=== here's the thread ... 2/2/2009
b) I had put in a new alternator & belt drive system a couple of years ago (need to check) <=== here's the thread 7/26/2010
c) I had put in a new battery just over a year ago (need to check) <=== here's the thread ... 9/19/2011

I think this is the drill:
Step 1: Disconnect & charge the battery
Step 2: Get the battery and alternator checked out at Autozone
Step 3: If it passes step 2, start looking for parasitic drain by pulling the FSU or its 40A fuse F76 (under the glovebox)
Step 4: If it's not the FSU, then start pulling all 88 fuses, one by one, with an ammeter in series with the battery
For your troubleshooting sequence, I would recommend pulling the FSU first rather than pulling fuse 76 for the following reasons:
1. Pulling fuse 76 will only determine if the problem to the heater blower circuit. This is helpful if we have no idea where the problem arises. But this problem (battery drain) is a somewhat common occurance in e39s.
2. The FSU has historical precedence for causing battery drain. By pulling the FSU, you might identify the cause of the problem immediately.
3. The FSU is much easier to access than fuse 76

If your current FSU is the problem and needs to be replaced, this suggests that even newer model FSUs will not last forever. Good to know.
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