# Battery Light Problem



## MoonRiver (Sep 2, 2007)

The problem is I don't know why the battery light is coming on.

The car is a 2000 Pontiac Sunfire. I've had the problem for close to 3 years. When the car is cold and I start the engine, the battery charge light comes on for several seconds. When car is under load, like going uphill or accelerating, the light comes on. 

During warm weather, the light stays on for a fairly short period of time. In the winter, the light stays on for 3 or 4 minutes before it goes off. It seems that as soon as the temperature guage moves off the coldest level, the battery light goes off.

The mechanic put a meter on it and said the alternator is putting out a good charge. I took it to Autozone and they put the machine on it, and even under load they didn't see a problem.

Have never had the battery go dead, so I know the battery is getting charged. Was going to take a trip through the mountains and am worried that the load will finally cause a failure.

Can someone tell me how to troubleshoot the problem?


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## agmantoo (May 23, 2003)

I realize the alternator is charging the battery. I would like to know that while the light is on what the voltage reading is at the battery. You need a digital VOM that has been calibrated and verify to the nearest 1/10th volt what the reading is. IMO the battery is just marginally being charged above 12 volts and when the vehicle is first started the load of the start drops the voltage further. It then takes the alternator a bit to get that draw on the battery replaced. During this interval the light is on. Once the battery is brought back to its charged state the light goes out because the voltage is now sufficient to cancel the light. This problem IMO is caused by the voltage regulator in the alternator.


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## MoonRiver (Sep 2, 2007)

Thanks agmantoo.


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## Bearfootfarm (Jul 13, 2006)

It could also be just a dirty electrical connection making intermittent contact.

I had a similar problem once, and after a lot of looking, finally found a wire that had some of the insulation rubbed off, and it would sometimes short out


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## Wis Bang 2 (Jan 12, 2010)

In the days of generators, dad would tune the car and set the idle low so the lamp lit at an idle...

Cars w/ undersize pulleys installed by horsepower freaks can do the same, the smaller pulley slows the charging rate at idle. Alot of gearheads found out that the needed toleave the alt pulley normal size to maintain the voltage level to drive the increased amps for their mega sound systems.

Drag racers use undersize pulleys as they operate mostly in the upper RPM ranges where the smaller diameter pulley doesn't matter.


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## Beeman (Dec 29, 2002)

Since you can duplicate the problem duplicate while you have a volt meter on it. When the light isn't on there is no problem so everything seems normal. Has the check engine light come on? Has anyone hooked a scan tool to it and read codes or live data? 
What does your owners manual say about that light coming on? I can't remember what all of them monitor. I have also mistaken one symbol for another and what I thought was one symbol turned out to be a low coolant light that came on cold and when going up hill.


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## MoonRiver (Sep 2, 2007)

Beeman said:


> Since you can duplicate the problem duplicate while you have a volt meter on it. When the light isn't on there is no problem so everything seems normal. Has the check engine light come on? Has anyone hooked a scan tool to it and read codes or live data?
> What does your owners manual say about that light coming on? I can't remember what all of them monitor. I have also mistaken one symbol for another and what I thought was one symbol turned out to be a low coolant light that came on cold and when going up hill.


On the 2 occasions I had someone look at it, the light wouldn't come on (of course). Autozone put it on the scan and even under stress couldn't duplicate the problem. 

Anyone want to make a guess as to the lifespan of an alternator? Being as the car is about 11 years old, I am thinking I might just bite the bullet and replace the alternator. It seems like there is a better than 50% chance that will fix it. I plan on keeping this car for another 10 years anyway. It's my convertible for drives in the country.


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## clovis (May 13, 2002)

Ooooh, a Sunfire convertible! 

I like!!!!!!


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## clovis (May 13, 2002)

MoonRiver said:


> On the 2 occasions I had someone look at it, the light wouldn't come on (of course). Autozone put it on the scan and even under stress couldn't duplicate the problem.
> 
> Anyone want to make a guess as to the lifespan of an alternator? Being as the car is about 11 years old, I am thinking I might just bite the bullet and replace the alternator. It seems like there is a better than 50% chance that will fix it. I plan on keeping this car for another 10 years anyway. It's my convertible for drives in the country.


Original alternators can easily last 200,000 miles, especially the AC Delco alts that GM uses.

I personally don't think that swapping an alternator (ie throwing money at it) is the right answer.


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## Beeman (Dec 29, 2002)

Did you look at the light closely to be sure it is the battery light? The symbols they use aren't always clear. 
I wouldn't replace the alt. just on a guess. Chances are the orig. alt. you have is better then the reman. you will replace it with.


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## MoonRiver (Sep 2, 2007)

Beeman said:


> Did you look at the light closely to be sure it is the battery light? The symbols they use aren't always clear.
> I wouldn't replace the alt. just on a guess. Chances are the orig. alt. you have is better then the reman. you will replace it with.


It's definitely the battery light. I watched it today. The car had been sitting for about 80 minutes. Started the car and turned ac on. Battery light stayed on for about 30 seconds.


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## Beeman (Dec 29, 2002)

Is there a starter alternator shop in your area? I would look for someone that specializes and is knowledgeable, not easy to find.


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## ponyboy123 (Jun 5, 2006)

replace the alt, if the problem continues the fault is smoe where in the charging system.


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## Danaus29 (Sep 12, 2005)

Are your connections and battery posts clean?


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## HermitJohn (May 10, 2002)

I'd make sure hot idle speed (rpm) under load is spec. My old F250 with the big six idles around 500 to 600rpm for hot idle. The alternator seems to need over 900rpm for idiot light to go out. So I just got used to idiot light coming on when idling at stop lights. I could just increase idle speed, but dont see a reason to. Once I got used to it and understood why it was doing it, its no big deal. Keeps battery charged just fine. If you are really worried, add a voltmeter gauge. When running voltage should be 14 to 15V. Having both a voltmeter and an ammeter is even better, but the ammeters commonly available arent heavy duty enough to deal with modern higher amp charging systems. Rule of thumb, if you have 14V with engine running and your headlights are bright, you are good to go.


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## foxtrapper (Dec 23, 2003)

How is the belt? I'd be suspicious of the belt being loose, worn or glazed. If you can't remember when the belt was replaced, I'd suggest spending the $20 or so on a new belt, and making sure it's adequately tensioned.

Just because you don't hear it squealing does not mean it can't be slipping.


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