Battery drain from Fuse 21... WTF?

[Das Delfin]

There are a couple other fuses which share circuits with fuse 21. The first that caught my eye was fuse 10 which also maintains the OBC and SI board, and the reverse lights. Since the reverse light switch has been known to cause current draw (either from corrosion of the plugs or failure of the switch) I would check there. Unplug it and see what happens to your draw!

Fuse 27 is also linked to the OBC but #10 sounds more likely to be related

[CorvallisBMW]

There are a couple other fuses which share circuits with fuse 21. The first that caught my eye was fuse 10 which also maintains the OBC and SI board, and the reverse lights. Since the reverse light switch has been known to cause current draw (either from corrosion of the plugs or failure of the switch) I would check there. Unplug it and see what happens to your draw!

Fuse 27 is also linked to the OBC but #10 sounds more likely to be related

I've checked 10 before and never seen a draw through it, but I'll check again. Can't hurt.

Upon doing some more digging in to the instrument cluster, I found that 50mA of the draw was coming from something in the cluster and another 100mA was from the Econoboost gauge. Since neither of those need to be always-on, I cut the red/green power wire that goes in to the blue plug and spliced in a switched, fused 12V source. Now the IC only gets power when the key is on, eliminating 150mA of draw. It doesn't solve the root cause, but it works for now.

I still have 100mA of draw on duse 21, but for now it's much better. I also had to buy a new battery since mine was about 70 months old and had been drained flat so many times that it was only putting out around 400 CCA.

[AndrewBird]

What voltage does it say on the si batteries? When fully charged, batteries will have a much higher voltage than their "nominal" voltage. If the batteries are 3.1 volt batteries, then they are probably bad.

[CorvallisBMW]

They were both at 3.1V and held there for days without discharging.

[James Crivellone]

Try this:

[iPee]

I think it's likely the SI Board. I had about at 80mA draw with a bad SI board and the batteries measured 3.1V as well.

http://www.r3vlimited.com/board/showthread.php?t=354672

Tested current without cluster 25mA
Tested current with cluster 25mA
Tested current with cluster + SI Board 80mA

[88BlackS-ETA]

I just had a drain on that fuse and it was my trunk light switch. I know you already checked that. The way I traced my drain was to have someone hold the multimeter terminals to a fuse and started to unplug everything the fuse supplied power to and it took me 5 minutes to find the problem. I unplugged the doors and all before I thought of the trunk lights might be the problem even though they were "turning off" with the trunk closed.