'00 Alero battery light, got charge.

Good afternoon,
My girlfriends '00 Olds Alero keeps throwing on the battery light. It appeared to happen at random times, only while driving.
Idle voltage is good, mid to high 13's, if I remember correctly.
We had the battery and charging system tested at a shop by some complicated machine that ran through a number of tests. Everything checked out just fine.
About a week later, we learned how to duplicate the problem... All you have to do is slow down to a lower speed, and accelerate with more than half throttle or so. Either that, or just bring the tach over 3500-4000 rpm.
I tried to read the voltage out of the cig-lighter while my g/f drove the car. It appeared that the voltage would slowly climb from low 14's, to about 14.3 or slightly higher while driving rather normally, where the battery light would decide to come on. I never solidly caught the voltage dropping off below the 13's or doing anything funny. Bumpy roads made me 'lose connection' a few times.
I'm pretty well lost from here as to what to do about this. Is 14.3 or 14.35 too high of a voltage for this vehicle?
Think it's the battery light circuit?
Voltage regulator? (Built into the alternator, right?)
The car has a 3.4L V6, w/60K miles on the clock. All connections look good. Battery cable terminals are oxidated, but not heavily corroded. As far as I know, untouched from factory.
Thanks, -marc
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Possible battery internal shortage would be my guess. Try swapping it with a known good battery and see what happens.
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"Bonneville" wrote:

Good idea...
I'll have to see when I can get under the hoods of both our vehicles.
Thanks, -marc
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Sounds like the belt may be slipping. If it has a tensioner make sure it is not binding...

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We exsperienced the same problem with our 99 Century Limited. Same engine, 3.4 liter.. Well the dealer said it was the alternator. It was replaced under warranty..

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Jay Smit wrote:

Thanks everyone.
I checked the tensioner, and it's good. The belt is probably about 10K miles old, and it's not glazed over or anything.
I'll clean up the battery posts tonight to make sure they're okay.
I got a few emails pointing to the voltage regulator or the alternator itself.
Since the alternator is putting out power, would it be worthwhile to go and buy a voltage regulator and just swap that part out, instead of $150 for the whole alternator?
Do you think a parts store could find a problem if I pull the alternator, and bring it into the store so they can spin it up on their little machine? I'm not sure it'll duplicate the higher rpm's it takes to throw the light.
-marc
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The battery light is generally a fault indication from the alternator itself. Even if the alternator is putting out power, it could have one of three diodes or windings blown or something, which will reduce its output capacity.
The Delco alternators aren't considered field rebuildable. I think there are some replacement parts available from the aftermarket, but my understanding is they're a pain to try to replace parts in.
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Marc Westerlind wrote:

We got everything sorted out last night.
I hope everyone has a good sense of humor.
It never was the battery light. It was the freakin low-coolant light. It took someone in a garage to tell us that, after running more diag- nostics on the battery and charging system. I wanted to just crawl under the car and hide.
This would explain why the light would only come on when the car acelerated hard though. Hah...
I consider myself a fairly good home mechanic... doing things from motorcycle engine rebuilds to cam installs. But something like this makes me want to reconsider ever picking up a wrench again.
Sorry for the false alarm, and thanks for the help. -marc
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