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Voltage regulator Posted by Ari [Email] ![]() ![]() In Reply to: Update: Battery light come on very dim, romick, Wed, 30 Mar 2005 05:23:10 Members do not see ads below this line. - Help Keep This Site Online - Signup |
My first guess would be the voltage regulator is on the way out. The brushes are part of the regualtor, so if you replace the VR, you get new brushes as part of the deal.
Here's a question - when the battery light comes on dim, what does the EDU voltage read? I assume it is in the 10-11 volt range.
I can speculate on why the temperature has an effect - the VR is temperature compensated. It reduces output voltage when it gets warm. Now, the VR isn't part of the cooling system, but if the temp gauge gets into the normal range, you figure the engine is at temp and radiating heat. The problem could be a poor brush connection, and the lowering of voltage by the VR could be enough to get the light on. Or, the brushes are fine and the temperature compensation has gone wacky. Or none of the above.
Assuming you're reading a low voltage, my first step would be to replace the VR. That way, it doesn't matter which of 5 different VR failure modes it is.
If that doesn't do it, it may be a diode in the alternator is failing when it gets warm. The test there would be to get the car warm, and have an automotive shop / many parts stores check the alternator. It takes a special tool (oscilloscope) to see that problem. If the diode is bad, the easiest solution is to put in a rebuilt alternator. Easily bought for about $125 or so. And take your new VR out of the old alternator before turning it in for the core charge. You'll have a spare VR, which isn't a bad thing.
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