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Wolfgang, VW Master Technician
Category: VW
Satisfied Customers: 4711
Experience:  Senior VW Master Tech 15 yrs
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2008 Jetta 2.5... Intermittent to constant no-charge. 3rd

Customer Question

2008 Jetta 2.5... Intermittent to constant no-charge. 3rd alternator, 2nd battery...I'm lost JA: Have you tested the battery with a voltmeter? And can you see if it's leaking or not? Customer: It shows 13.6 after a charge... I haven't tested when the car freaks out on highway or quits, the key tells me it's dead. JA: Are you fixing your Jetta yourself? What have you tried so far? Customer: I am. I'm on my 3rd alternator and second NAPA battery. JA: Anything else you want the mechanic to know before I connect you? Customer: I don't believe so.

Submitted: 5 months ago.
Category: VW
Expert:  Lou P. replied 5 months ago.

Hello, my name is***** and i will do my best to assist you.I am going over your story now and will reply back soon with some info,thanks!

Expert:  Lou P. replied 5 months ago.

do you have a volt meter to check the battery while the car is running to see what the voltage is?

Customer: replied 5 months ago.
I do yes. After an external charge, it's 14.2; after an hours drive with NOTHING on (radio, fan, etc) it's 12.2.
Expert:  Lou P. replied 5 months ago.

ok , the biggest issue is melting fuse boxes, on top of the batter you should have small fuse box with a bunch of red and or black wires coming out of it , ill send a picture over, this box powers the alternator. most times the fuses blow or the box melts.

it also affects the ac compressor and radiator fans if memory serves me., so take a look at this box, we used to change the fuse box and the wiring to the alternator . very very common issues. hope this helps. let me know, I will do my best to help you. Please take a second and click the stars at the top of the screen to rate me so i may receive my credit , 5 stars is ideal , please request me in the future.
Keep in mind then when you rate it does not end our conversation. you can still return here to me for follow up information if needed, Lou P.

Customer: replied 5 months ago.
Thank you... My fuse box there is in good shape. What I did notice last evening, is that most of the time, when I return to idle it charges and the warning lights in the dash go away... I'm thinking voltage regulator? IF that's it, can one possibly get it off the back of the alternator without removing the alternator...which requires removing the intake manifold...?
Expert:  Lou P. replied 5 months ago.

interesting,,,,,,,,, usually returning to idle is worse, you dont hear a belt squeal do you? a loose tensioner can cause something like this cause the belt will slip on the pulley of the alternator. I do not think there is enough room to get the regulator out, plus you have changed the alternator so that should have been fixed as well with the new alternator.

Customer: replied 5 months ago.
No, there's no squeal. I suppose I could shoot some dressing on there and see. It's on its third alternator. The original, a replacement, now a rebuild of the original (reputable shop). It' s also on it's third battery (original, new from NAPA, replacement new from NAPA). I requested a warranty on the battery after one of the alternator fails. Seems I get 3-5 months out of an alternator.
Expert:  Lou P. replied 5 months ago.

hmm, i really suspect the fuse box, can you open it and send me a few pictures of it. ?

Customer: replied 5 months ago.
I can, but it will be this evening. I didn't drive it today... I'll follow-up for sure. I appreciate your help.
Expert:  Lou P. replied 5 months ago.

no problem, we can get this figured. also is your car auto or manual? that actually may matter.

Customer: replied 5 months ago.
It's an automatic...
Expert:  Lou P. replied 5 months ago.

ok, the manuals have a clutch inside the alternator. not sure if the automatics do . not 100%

Customer: replied 5 months ago.
Gotcha... I'll send pics of the fuse box tonight.
Expert:  Lou P. replied 5 months ago.

ok sounds good.

Expert:  Lou P. replied 5 months ago.

checking in, havent heard from you in a few days. you still need my help? I am here if you do.

Customer: replied 5 months ago.
Sorry for the slow reply... BTW - this is a 2008 Jetta - not sure how I typed 2005 in the title. I have confirmed that it charges at idle to 1400RPM then no more. I've attached photos of the fuse box nonetheless.
Expert:  Lou P. replied 5 months ago.

ok, that fuse box is the different one. I will have to opt out , this later year I am not sure of the issue and dont want to waste any more of your time.

Expert:  Wolfgang replied 5 months ago.

Thanks for choosing Just Answer . I'm Wolfgang here to help!!

I am confident we can resolve your problem together. Please
understand that I don't know your skill level. In most cases when you have a problem
with the way the vehicle performs, specialized tooling is required to acquire computer
data/information or engine testing results. We didn’t build these complicated vehicles; we
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ok i see what is going on. i need you to do this .

  • car running i need you to monitor the voltage on the back of the alternator as it warms up and see if the voltage goes down or not. do this for 30 minutes with the high beams and fan full high.
  • if not then check at the black cable that goes to the fuse box all the may on the left as you facing. measure the voltage there.

please let me know what you come up with please


Customer: replied 5 months ago.
Thank you for the quick reply... I have a voltmeter in the cigarette lighter, it mirrors what the multimeter shows on the area circled. It kinda charges at idle, and drops as idle increases over 15-1800rpm. At its very best at idle, it will show 14.2, but usually 13.2-13.9.
Expert:  Wolfgang replied 5 months ago.

that test at the cig lighter will not work . you need to check the voltage at the back of the alternator with a volt meter and then at the circled area of the pic you have provided. i need to see if the voltage is different at the back of the alternator to the cable point of the fuse box.


Customer: replied 5 months ago.
Not sure where I can get on the back of the alternator the way it's tucked up there. Any pics?
Expert:  Wolfgang replied 5 months ago.

yeah not easy to get but need to get to it . i usually get a long screwdriver and then use that with one lead of the meter touching the blade of the screwdriver to the nut of the big cable of the alternator . note be careful not to ground the blade to metal or damage will occur.

Expert:  Wolfgang replied 5 months ago.

any update?

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if not.....

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