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DIY: Do It Yourself
Post here to share or improve your wrench turning skills! All BMW E46 DIY tips, tales, and projects discussed inside. Learn to work on your car and know the right BMW parts you will need!

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Old 12-06-2014, 01:32 AM   #1
angstadt530
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Join Date: Aug 2007
Location: USA
Posts: 82
My Ride: 2003 BMW 330i
Battery light caused by oil level sensor blowing fuse 30

My red battery light was on the past few weeks even though the voltages were fine. It turns out it was caused by a bad oil level sensor that was blowing fuse 30. I've been doing a lot of research the past few weeks and I didn't see many stories quite like mine, so I thought I'd share:

What tipped me off to this was the yellow oil level light would come on maybe 10-15 seconds after start, then go away about 5 seconds later, even though the dipstick showed I had plenty of oil. I read this tends to be an indication the oil level sensor is faulty, and to check fuse 30. Sure enough, it was blown, and it would blow again each time I turned the car to "on", even if I didn't start it.

(Note: The definitive test for this is to unplug the oil level sensor, turn the car to "on", and see if the fuse blows. However, to reach the plug you need to raise the car, remove the splash shield, and remove the reinforcement plate, so it's not exactly a quick test.)

The alternator happens to be on the same circuit as the oil level sensor, so if that fuse blows, it must mess with the battery light somehow, even though the alternator works fine with the blown fuse.

I replaced the oil level sensor and fuse 30, and the red battery light finally disappeared from my dash after start! In the process of debugging this I had first replaced my voltage regulator, then the entire alternator, as well as the battery and a couple pulleys that didn't have much life left. Given the age and wear of those items I don't regret replacing them (let's call it preventative maintenance), but I sure would have saved some money and avoided some anxiety had I known to check the oil level sensor from the start.

So if your battery light comes on but your voltages look normal, check fuse 30 and watch for the yellow oil level light during the first 30 seconds after you start your car.
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alternator, battery light, fuse 30, oil level sensor, voltage regulator

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