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Low Voltage Light

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GreenPrix99

New member
Hey, I recently purchased a 99 Grand Prix GT. Not many problems with it, until recently the low voltage light has been coming on (The little light that shows a battery low on fluid). It would come on while driving then shut off for a while and randomly go on and off while driving. It seems like the problem is getting worse, as the light seems to come on right after start up and stays there a long time, it will still go out eventually, but not for very long.
The car has a brand new serp. belt and brand new battery in it, so I am thinking the problem is my alternator. Unfortunately I don't have a voltmeter to test it, and i am on a very tight budget so I don't want to pay to have someone test it. I was just wondering if you guys thought it could be anything other than my alt?
 


Most chain parts stores will test your changing system for free. Places like Autozone, Advance Auto, Checkers, etc. Take it there and have them check it.
 
battery low on fluid light.....lol sorry i had to say it....if ur battery is new if you take the positive {RED}wire or of the batery terminal and the car dies then its your alt..thats another way to test it if you dont have a meter..
 
bigdawg15005 said:
battery low on fluid light.....lol sorry i had to say it....if ur battery is new if you take the positive {RED}wire or of the batery terminal and the car dies then its your alt..thats another way to test it if you dont have a meter..
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Wait, are you suggesting that he disconnect the battery when the car is running?

Um, I don't think that is such a good idea for a whole list of reasons.

But I am hoping I just mis-read or mis-understood your suggestion.
 
bigdawg15005 said:
battery low on fluid light.....lol sorry i had to say it....if ur battery is new if you take the positive {RED}wire or of the batery terminal and the car dies then its your alt..thats another way to test it if you dont have a meter..
Click to expand...

You can't trust that method with newer cars. Some have built in safety measures that will kill the car if the battery is unhooked. Also, you chance maiming your PCM.

OP, go have your charging system checked. Usually a light like that is a sign of a failing or failed alternator. It's also possible that you simply have a loose wire somewhere in the charging system.
 
Hey thanks for the replies everyone. I found a friend with a voltmeter and the battery is reading 12.8 volts with the car off and 14.5 with it on, so I have no idea what's wrong :th_scratchhead:
 


DanGTP said:
You can't trust that method with newer cars. Some have built in safety measures that will kill the car if the battery is unhooked. Also, you chance maiming your PCM.

OP, go have your charging system checked. Usually a light like that is a sign of a failing or failed alternator. It's also possible that you simply have a loose wire somewhere in the charging system.
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Im not talking about most cars im talking about his gp...ive done it hundreds of times.it would just be like if the battery when completely dead what would the diff be plz inform me...and if it did your telling me it would fry the comp??i doubt it...I didnt say disconnect the terminal and throw it around the engine bay....or ground it out on somthing..all you do is loosen it and quikly lift it off and if it starts to die press it back on. if it does start to die its your alt if it stays running its your battery then you get which ever it is tested just to double check. its an old mechanics trick.....i guess you learn somthing new everyday bc i didnt know there was any sensor incase the battery was disconnected guess its on the same car with the battery fluid light idk lol....i know a lot of things are electronicly controlled on the newer cars but this trick does work and will help if done properly...im not saying its the best way to do it a meter or tester is always better but doing this trick WILL point you in the direction needed to start diagnostics.....Ive had the main positive wire on my 2001 truck short out on the body meaning it was routed through the body panel and from vibration cut itself totally groundint out and didnt fry a single sensor or anything so i doubt doing what i said will hurt anything...and again im not saying to throw it around the engine bay....good luck guys....

If you cant manage to do this on your car/truck then u def shouldnt even open the hood..... no offense to the op...
 
bigdawg15005 said:
Im not talking about most cars im talking about his gp...ive done it hundreds of times.it would just be like if the battery when completely dead what would the diff be plz inform me...and if it did your telling me it would fry the comp??i doubt it...I didnt say disconnect the terminal and throw it around the engine bay....or ground it out on somthing..all you do is loosen it and quikly lift it off and if it starts to die press it back on. if it does start to die its your alt if it stays running its your battery then you get which ever it is tested just to double check. its an old mechanics trick.....i guess you learn somthing new everyday bc i didnt know there was any sensor incase the battery was disconnected guess its on the same car with the battery fluid light idk lol....i know a lot of things are electronicly controlled on the newer cars but this trick does work and will help if done properly...im not saying its the best way to do it a meter or tester is always better but doing this trick WILL point you in the direction needed to start diagnostics.....Ive had the main positive wire on my 2001 truck short out on the body meaning it was routed through the body panel and from vibration cut itself totally groundint out and didnt fry a single sensor or anything so i doubt doing what i said will hurt anything...and again im not saying to throw it around the engine bay....good luck guys....

If you cant manage to do this on your car/truck then u def shouldnt even open the hood..... no offense to the op...
Click to expand...

Wow, that was hard to read.

But no, on today's newer computer controlled vehicles, disconnecting the battery while the car is running in not advised. In the older days when vehicles had less electronics and were not as sensitive to voltage fluctuation, this was not an issue. I remember my dad doing it on our old 71 Jeep. But with today's sensitive PCM and electronic injectors and sensors, disconnecting the batter while the alternator is trying to charge the system can result in a very sharp voltage spike. This can definitely cause issues with your PCM, injectors, and other sensors.

So again, while this may have been an old mechanics trick from years ago, it is not recommended on today's newer computer controlled vehicles. Please don't offer this advice anymore.
 
^ Well said. I've sold many a PCM to people that have tried that trick. That's how I know. Never bothered trying it to my own car...

GreenPrix, a voltmeter won't necessarily tell you if your alternator is good or not. The voltages you gave are indicators that there is some charge coming from the alt, but you won't know how many amps are moving through the charge wire. The voltage difference between the alternator output and the battery's nominal charge value is what allows the battery to be charged. The amperage is how well it is being charged.

If your electrical system is trying to use 80 amps, and your alt is only putting out 30 (even though it's 14.5 volts), the rest of the power has to come directly from the battery, causing a drain (This situation can also cause an alternator/battery light to come on). BTW, if you have the alt tested, it should put out AT LEAST 84 amps under load (80% of its rated output).
 
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