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How can you test if your alternator is not working?

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Old Feb 7, 2010 | 09:40 AM
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Default How can you test if your alternator is not working?

I must know.
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Old Feb 7, 2010 | 10:01 AM
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Bring it to Autozone?

Jonny
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Old Feb 7, 2010 | 12:39 PM
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1. start your car first
2. then unhook your battery.

the alternator should power your car while its running if its not bad. give it a few minutes to test. if the engine shuts off then your alternator is bad. also check if there is oil dripping from above it because oil could leak down on the alternator from the distributor making it go bad.

hope this helps
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Old Feb 7, 2010 | 02:57 PM
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Originally Posted by clownin
1. start your car first
2. then unhook your battery.

the alternator should power your car while its running if its not bad. give it a few minutes to test. if the engine shuts off then your alternator is bad. also check if there is oil dripping from above it because oil could leak down on the alternator from the distributor making it go bad.

hope this helps
+1 ran this test for a fact in my bros celica. brand new alternator from kragen went bad after a year. took it back and got it replaced for free
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Old Feb 7, 2010 | 07:20 PM
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The car actually shuts off on me while running. I can't start it up now because the battery is totally drained.

I had the volt light on before it turned off on me. I jump started it twice and it would not keep a charge after starting. I guess that totally means that it's the alternator, right?
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Old Feb 7, 2010 | 07:22 PM
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That's right. If the engine is on and dies disconnecting the battery, it's the alternator

I believe you may be able to take to autozone or something and charge the battery there
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Old Feb 7, 2010 | 10:07 PM
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Do not ever disconnect the battery whilst the car is running.

The alternator uses the battery sense wire to determine the level of charge and therefore the alternator output. If you open circuit the system the alternator can overcharge and blow diodes in the rectifer.

The correct way to test an alternator is to place a load on it, fans, lights etc and measure the output voltage using a multimeter. It should be about 14.2 volts all the time.

Matt.
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Old Feb 8, 2010 | 05:38 PM
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I'm guessing this is what's wrong with mine. Drove great up until I would use the brake and then the power would drain and kill the car, or if I was using the stereo it would die. Good to know it might not be a wiring ghost.
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Old Feb 8, 2010 | 06:14 PM
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I think Advanced auto or autozone can run both of these test on your car actually to test the battery and the alternator. They test the alternator with the battery in the car, and test the battery while its out of the car.
They don't really like to do these tests but if you are persistent they should, especially if you say you want to buy a battery/alternator.

Last edited by Ali SC3; Feb 8, 2010 at 06:27 PM.
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Old Feb 8, 2010 | 06:34 PM
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mine just died on me yesterday...

the battery light kept coming on while i was driving, my volt meter on my timer and headunit was only at 11.5v when i started driving and ended up at 10.7 when i got home. i shut off the car and tried to start it back up... and it didnt
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Old Feb 8, 2010 | 06:37 PM
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can the alternator go bad w/o the battery light going on? I didn't see mine flash though it could have
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Old Feb 9, 2010 | 04:59 AM
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+1 Mattman, use a DC volt meter accross the battery posts, unhooking cables with engine running is not good, can mess up alternator & ecu.
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Old Feb 9, 2010 | 04:16 PM
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simple test.

Take battery voltage with a volt meter with the car turned off. SHould be near 12v. Turn on the car and while its running check the battery. SHould be around 13-14v. If its still under 12 volts your alternator is not charging your battery
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