is it my alternator or battery?

[LuxurySport00]

i'm guessing it's the former.. i was at a traffic light and was closing the window and noticed the headlights dimmed a bit. i tried again when i was in my driveway and sure enough, any extra juice and they dim. then to top it off i went to turn on the AC and the car died. i was able to turn it back on, however.

 

[Quik LS]

sounds like alternator to me.

if the cars running then the alternator should be able to keep up with the demand (unless you've added a bunch of stuff) - if the car can't start then more likely the battery.

You should be able to jump a car with a dead battery and drive it around - right?

 

[BanginLS]

im with quick... prolly the alternator.. but i would test the battery first.. if batteries never went bad then they wouldnt sell them almost everywhere...


u can even go as far as recharging ur battery to see if thats the problem.. it could also be the mods u have made.. do u have HIDs, system etc..? if u do u may need a cap or a seperate battery.. it all depends

 

[TheRebel]

A quick test you can run if you have a multimeter is check your battery with the car off. It should read 12 or more volts. If not then then it is bad. If it is good start your car and measure the battery again. It should be at 14V or more with all your accs off. If not then you alternator is prolly going bad.

 

[2002_LS_V8]

i had a civic that did that, after i changed the battery it was all O.K.

 

[Wishmissle]

sounds like the alt is dead..if it runs when you jump it off....disconect the battery. If it dies, the alt is dead.

( the battery will be drained if the alt died BTW )

 

[Jim Henderson]

sounds like the alt is dead..if it runs when you jump it off....disconect the battery. If it dies, the alt is dead.

( the battery will be drained if the alt died BTW )

This is an old trick that was usually safe back when cars had fewer electronics. I would not recommend disconnecting the battery while the car is running since the battery acts like a filter. If you get some noise spikes or a surge in voltage, you might toast some pretty expensive electronics, like the computer or the stereo etc. Doesn't happen often but once is plenty expensive.

Better to use the meter and check the voltages while turned off and while running. You might also notice a surge as someone increses the engine speed.

I believe the normal off voltage is around 12.8 or a little more with a fresh battery. 12volts usually indicates a weak battery. Running with all accessories off should be about 13.8 to maybe 18volts although that makes me nervous. As more accessories and things like lights are turned on, you might see the voltage drop but unless you have added a horking big stereo or are lit up like the Eiffel tower, you should not drop much below maybe 12.xx volts.

BTW a lot of battery shops will do a free alternator and battery load test for you. Most of them won't scam you for a battery or alternator unless the test shows obvious problems.

Good Luck,

Jim Henderson

 

[beaups]

you should get it checked as these batteries have been known to malfuntion internally (not just die) and cause similar problems that would otherwise point to an alternator failure. Additionally, on the LS the PCM manages the alternator duty cycles so it could be even more complicated (albeit not likely) than an alternator or battery.

 

[2001LS8Sport]

A quick test you can run if you have a multimeter is check your battery with the car off. It should read 12 or more volts. If not then then it is bad. If it is good start your car and measure the battery again. It should be at 14V or more with all your accs off. If not then you alternator is prolly going bad.

This is true....but you must charge your battery before you can properly test it. I can promise you it will check bad in it's present condition. A fully charged battery with no load should check at 12.6 volts with the surface charge removed (by turning the headlights on for a few minutes prior to checking voltage) Each cell in the battery should produce 2.1 volts. But to properly check the battery, you either need a load tester or a hydrometer. I'm guessing it's alternator. But a voltage check of the alternator is only a partial check. It too should be checked with a load. I have seen alternators that would put out voltage, but no amperage.

And by the way, I agree.....NEVER disconnect the battery with the car running. The voltage spike can severely damage the electronic components on the car. Most have diodes to protect them...but if they are bad, or overloaded, it's bye bye component.