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My battery light came on, and has been on, all day today while I have been driving. I know this usually means bad alternator, weak bateery, or loose wires somewhere.

So I bring out the DMM and do some testing. After I first noticed the battery light come on, I have to drive about 5 miles to home. Figure the battery (Optima Red Top, about 8 months old) would show a decent amount of voltage loss if the alternator was bad. Put the DMM on it, and about 13v..... weird.

Start the car up, test the voltage on the battery again..... 14.5v.... double weird. The alternator is running fine, putting out full power. I turned on the radio, headlights, AC, etc, and hardly any voltage drop at all (nothing that would warrant a bad alt).

Check all wires, power ground, etc, and everything is fine. I have now driven for about 60 minutes or so with the battery light on. When I turn the car off, battery still reads about 13v.

So WHY THE HECK IS THE BATTERY LIGHT ON?

also, I have turned the car off and restarted multiple times, and the light is on everytime. The car has no problem whatsoever turning over, starts like usual. I'm starting to think there might be a problem with the bulb for the battery light!

start the car pull the wire on the batt and see if it keeps running. the alt might show 14.5 v but may not have any current behind it

this is a sign that your sub isn't for you.

send it to me. =)

there are no subs in the vehicle.....

what do you mean no current behind it?

amperage

You should have narrowed the problem (if it was cause by lack of amperage) when you turned everything on, and shot for voltage. But Bills test will take it a little further. So I would give it a try.

I would try taking the ground loose and leaving it for a few min. There could be a fault in the computer that needs reset, and thats why your still getting the light.

Why I didn't think about resetting the CPU is beyond me. I'll try that tomorrow.

JeremyC wrote:You should have narrowed the problem (if it was cause by lack of amperage) when you turned everything on, and shot for voltage. But Bills test will take it a little further. So I would give it a try.
I would try taking the ground loose and leaving it for a few min. There could be a fault in the computer that needs reset, and thats why your still getting the light.

You shouldnt unhook your battery cable when the vehicle is running, computers, amps and other electrical items dont like that very much. Plus, this can actually kill a good alternator...

Also, alot of times just unplugging your battery cable wont reset the codes, sometimes it takes a scanner (but you can atleast safely try this one).

this may suprise people, but sometimes the battery light and other $hit come on for no reason at all.. like the Check Engine light.. you just got a tune up and all, and look, its still on.. rule it out all you want. but its still possible..

Yeah, sometimes when you throw a code its just a glitch, most of the time we arent that lucky though.

The fact of the matter is usually when the ses light comes on its due to a bad sensor, not because it needs a tune up... Although a bad plug, plug wire, cap or rotor bug (basic tune up) can throw a code... Most of the time its one of the stupid o2 senor.