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Battery Light at High Speeds

I noticed last week that when I am traveling to work, only when on I-80 at higher speeds, the battery light comes on in the Cavalier (1999). When I am on smaller roads, at slower speeds, it goes away. The light is not on the entire time I am driving fast, it comes on for a few seconds, then goes off, then comes back on, and goes back out. It doesn’t appear to be affecting anything else, but want to get it fixed so I’m not stranded somewhere. Battery is not very old and alternator was rebuilt within past two years. I do get a bit of a squeal from the alternator belt when the car is running. Do I just need to readjust the alternator or could it be worse?

More than likely, the serpentine belt is slipping when you see that alternator light.
I’m not sure if you can manually adjust the belt tension on this car, or if this is a case of needing to replace the belt tensioner, but I would suggest that you have this situation remedied before you wind up killing that battery.

I agree with VDCdriver. I have seen this problem a few times. A weak tensioner, worn belt or liquid on the belt like oil, coolant or water will cause slipping at higher rpm.

What would be the best way to figure out which one it is? Could I spray something on the belt to remove the oil and then see if the light still comes on…and that would then point to the tensioner? It is an old car with 206,000 miles.

Do you have a mechanically inclined friend who could look at the vehicle for you? I would not spray the belt because it will probably add to the problem you already have. If you can remove the belt you can inspect it for cracks and worn areas. Pay attention to the spring pressure on the tensioner and check the bearing on the tensioner pulley. It should not have any play in it.

I do have a friend that works on cars. He just finished rebuilding a 68 Beetle not long ago. I’ll have to visit him and see what he says. He just built a new garage anyway so that gives me a reason to visit. Thanks.

But based on what you are saying, the belt is slipping, which in turn isn’t charging the battery and triggering the light to come on, correct?

That is correct, Jimmy.

High RPM can also open defective armature windings (centrifugal force) causing these symptoms…It doesn’t have to be belt related, it could be the alternator itself…

How old is the belt?
If over 5 years old I’d just change it first.
I try to avoid blindly changing parts, unless it’s a cheap one that’s long in the tooth.

I’ve never changed the belt, but when the alternator was replaced, I do not believe he put on a new belt. I’ve had the car since 2001. Maybe it is time for the new belt, but to be honest, the squeal has been there for a while and I thought it was related to not adjusting the alternator to fit right when he put it back in. Ill try the belt first.

I see a high mileage type belt at Advanced auto - are those worth the extra $10?

I’d just get a “regular” belt made by a reputable brand like Gates or Goodyear.
I can’t think of other names, but I’m sure other posters will come up with more.

Since there’s a squealing I too would assume the belt is slipping due to age or a bad tensioner. The alternator light will also come on if the brushes in the alternator are worn out. If the belt doesn’t fix the problem I’d pull the brushes and see how they look.

My wife’s car had a similar problem. '92 Toyota Celica. Replaced the alternator last year when the original one quit working. Wife was on the freeway and the battery light goes on. Turns off as soon as she slows down for the exit. I went out to look at it, and noticed it only went on when the RPM’s were high. Broke out the volt meter, and the voltage was at 14.3 volts at idle. Stayed at 14.3 volts until the RPM got to 3500. Then, the voltage began to climb. at 5000 RPM, it was reading 18.4V.

That reman alternator had a defective voltage regulator. Took it back for a replacement. Replacement works as it should, no voltage increase at high RPM. Problem solved.

BustedKnuckles"Wife was on the freeway and the battery light goes on. Turns off as soon as she slows down for the exit." "That reman alternator had a defective voltage regulator."

A battery light coming on at high speed and extinguishing at low speed usually means a bad voltage regulator.

Bottom line:
You’re due for a new belt. Anfd the tension can be measured (and/or the tensioner checked) at that time.

Aldo, have your battery and alternator tested. Even though the battery isn;t too old and the alterbator was “rebuilt” within the last two years. By the way, was it rebuilt or the old one replaced with a rebuilt one? It would be highly unusual for a shop to rebuild it on-site.

Belt sprays are only good as a diagnostic tool, to see if in fact a slipping belt is a cause. They are not a cure.

My money is on a faulty alternator.

Mechaniker, that’s why I mentioned it. 7 people replied, and only one mentioned a failed alternator. But, none mentioned failed regulator.

The alternator and regulator are one unit…They are built together…