Alternator not charging battery

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Jun 7, 2009
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Ohio
I have a 2003 Jetta TDI with an alternator not charging the battery. In the past when I’ve had a bad alternator, that battery light illuminates on my dash. But this time, no battery light. What else should I check/troubleshoot before I replace the alternator?
 

outoforder

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Jun 7, 2009
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Ohio
How do you know it is not charging. Did you put an external meter on it to check? Before you replace it, you need to isolate that the problem is within the alternator itself.
The fan inside the car only blows at half speed and the headlights become dimmer as I drive. After I get home and turn off the car, it won’t restart without charging the battery.
 
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The fan inside the car only blows at half speed and the headlights become dimmer as I drive. After I get home and turn off the car, it won’t restart without charging the battery.
Plug in voltmeter, at the very least.

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JBP

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Jan 29, 2022
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Alabama
Exciter wire to the alternator could be broken or corroded also not allowing it to generate.
 
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Ok, so no you have not tested the alternator with an external meter. Go to AutoZone or Advance Auto. They can test it with a meter and determine within a high probability that the alternator has an issue.

This ^^^^^^^^^^^^^^^^^^^

I had this same exact issue with my truck a couple of years ago. (1991 F-150). I noticed the voltmeter was reading very low while I was driving. I had it tested at O'Reilly. The original alternator was shot. I installed a new one, took it back to O'Reilly and they retested it.

It was charging like crazy. The voltmeter reading was to the far right. (The "A" on "NORMAL"). Problem solved. Don't make work for yourself. Chances are it's the alternator. Take it in and they'll tell you either way in 5 minutes.

They like when you do this, because they don't give refunds on electrical parts once they've been installed in a car, by shade tree mechanics who throw parts at a problem hoping to find the solution.
 
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Jun 6, 2013
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I have a 2003 Jetta TDI with an alternator not charging the battery. In the past when I’ve had a bad alternator, that battery light illuminates on my dash. But this time, no battery light. What else should I check/troubleshoot before I replace the alternator?
Burned out light? It is my understanding an alternator requires a "boot up" current flowing through that bulb to begin charging. If that bulb is burned out- no charging. However, some systems have a resistor in the circuit to bypass a defective bulb. But check the bulb first
 
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May 7, 2020
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Ames, IA
My 02 Beetle has an external regulator on the back of the alternator that can be changed. I ended up putting a junkyard alternator on it due to time constraints.

Does yours have an external regulator as well?
 
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