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2004 Volkswagen Jetta

Question: how do u know if its the battery or the alternator

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Visitor, Indianapolis, IN, July 11, 2011, 20:42
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 Rookie

The red engine light on my car was on. My car sputtered and the radio when out. Steering was fine. I have never replaced the battery in my car. What can it be?

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  • Answer #1

    big01_dram July 11, 2011, 21:03
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     Journeyman

    The easiest way to tell is go to Autozone. They will do a test on your battery and alternator for free. If its the battery they will install it for free to. Unless its hidden in the fender like in a Dodge Intrepid. One way to tell it is the battery is on initial start up. If starting seems sluggish or you have to jump it its a good chance its the battery. Though If the alternator is not charging it can cause a similar situation. if you are interested I found this info on the battery and charging system operation. Know how it works can go along way to figuring out the problem. http://www.bcae1.com/charging.htm In any case the easiest thing to do is go get the free test while your vehicle still runs. Im betting on the battery since you have never replaced it.

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  • Answer #2

    Visitor, July 12, 2011, 14:43

    OK, first start your car, then pop your hood remove the positve battery clamp from your battery if nothing happends put it back on then remove the negative if your car cuts off it is your alternator. if it stays on it is your battery

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    big01_dram, July 12, 2011, 14:55
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     Journeyman

    Those test can potentially work. they are dangerous though. your battery is used for 2 things. For initial start up and as a voltage spike cushion. Your alternator puts out a range of voltage from 13.5 to 15.5 volts. Voltage this high will short your computer out. Then you have bigger problems. The computer needs a constant 12 volts to operate correctly. The higher voltage from the alternator so it can keep the battery charged. To maintain the 12 volt charge in the battery you have to have the higher voltage from the alternator. The battery puts this constant 12 volt supply out for the computer. Use these techniques at your own risk.

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