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'88 560 SEL , 01 540i
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301 Posts
Discussion Starter #1
Need some advice,
My battery light out of nowhere today started displaying with the engine off! Sometimes check engine light would illuminate too. Got the car home, plugged in the multimeter and ran some tests (full load, half load, no load). Alternator is putting out above 13V, so the charge was good. After these tests, battery light now off when engine is off, but now displays with engine on! Also, if I give the car gas, once the engine hits 1500RPM the ABS light comes on. Battery at 1500RPM was reading 13.4V, Checked the OVP and it looks bad (fuses are good, but pins on the bottom are in bad shape, one of them remained the in the black cable connector when I pulled it out). I will be ordering a new one tomorrow, but wanted to know if there is anything else that I should check?

Thanks.
 

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Registered
'88 560 SEL , 01 540i
Joined
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301 Posts
Discussion Starter #3
Update for future searchers:
Changed the OVP this morning with a new one, and the problem remained. Although it was good I changed it anyways, since it didn't look to healthy to begin with. On with the diagnosis - repaired alternator terminal connections which looked like crap too, and I thought perhaps resistance in the wires was causing the problem, but still no change. So I pulled the alternator from the car, took it to an electro-mechanic and discovered the diode plate was the culprit. Output was ok on the bench test, but the battery light on the bench tester was going off as well. So a new diode plate in the alternator solved the problem. Total cost, OVP = $70 , diode plate = $65.
 
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