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Old 11-12-2010, 03:10 PM
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bluebee bluebee is offline
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Location: San Jose, California
Join Date: Mar 2008
Posts: 25,236
Mein Auto: 02 BMW 525i M54 auto 130K
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.
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