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Just another Fuse 21 battery drain... well not really

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    Just another Fuse 21 battery drain... well not really

    Good morning, I have been chasing down a battery drain on my 1990 325i over the last year and have run out of ideas, looking for some help!

    I was able to narrow down the draw to fuse 21, so one by one I checked each possible load on this circuit and found none of the listed equipment on the circuit were causing the draw. Checked all lightbulbs, OBC, pulled the whole instrument cluster, etc.

    One interesting symptom is that the cabin blower stays on when the car is off and can be adjusted. Removing fuse 21 seems to cut power to the blower (I believe the blower should be on a different fuse). I removed and replaced the FSU which can be a culprit for this issue but the battery draw remains.

    At this point my only idea is that there may be a short to ground somewhere on the fuse 21 circuit. Any insights would be greatly appreciated, thanks!

    Trunk light?
    2004 525i Manual - 1985 325E Coupe Manual


      I've pulled every interior light and the draw is still there.


        The blower motor should not be operating with the key off so that is suspect. If your vents are pushed to the right, the blower could be running with the car off.

        Also, fuse 21 powers the SI board. They are very common to fail and cause the battery drain. I am almost 100% sure this is the cause of your drain, although with the blower issue, you may have two sources of drain. Your SI board will need to be refurbished, we deal with this issue many times per week.
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