2003 Volkswagen Jetta - Alternator

How do I determine if the alternator is bad on my 2003 Jetta?

With a voltmeter, check voltage at battery when car is running. Should be 13.5 - 14.5 volts DC.

Call your local Auto Zone if you are in the US and see if they will check it . If it is bad then you are running on the battery only and you cannot go far that way.

That is what I am going to do.

It’s at 12.66 with the engine NOT running, which is just right.

Thx for that.

I hope that that is what it is …

Thanks for the quick reply tcmichnorth!

I already did. They ran a test and it read that the voltage regulator was failing.

They are not always correct so I am going to do the voltmeter test.

The thing is that I live in a small town and don’t put many miles on the car, so the battery

may just need a good charge.

Thanks for the quick reply VOLVO_V70.

Not if it reading 12.66 volts, it doesn’t. That is a charged battery.


I tested with a 12V meter, although I read it supposed to be a 20V?

Anyway it came out at 12.06 not running and 13.89 running.

12.06V means the battery needs a charge. 13.89V running is OK, and low-normal, probably because the alternator is working hard charging the battery.

Nothing should be 20V.

The 20V came from a post on Advance Auto Parts site. AAP is where the alternator was purchased in 2013.

First read at AutoZone was “failing voltage regulator.”
So I went to local NAPA to see what it would read and it was 12.66.
Last nite at home with a 12V it was 12.06

So it looks hopeful that the alternator is ok and that I need to charge the battery because
it’s short local driving and the battery does not get fully charged?

20V?! :man_facepalming: Maybe they meant to set your voltmeter to read up to 20V? That would make sense if you have one that could read either 10 or 20 Volts…

Yes, I would agree with that.

Yes, it read to set it to 20V on AAP site. Sorry for not being clear on that. :slightly_smiling_face:

Last nite we set it to 12V, which was the highest voltage and we got the 12.06.

So I am happy that I just may not need a new alternator.


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