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Discussion Starter · #1 ·
I have a battery less than one year old from dealer.

I have a new B+ battery/alternator cable less than one year old. Replacing this gave me pretty constant 13.5V.

I have a 2004 V8 that was stone dead after three days of sitting at 15F.

At Idle the voltage hovers around 12V, but bounces around between 12V and 14V when driving.

Time for a new/rebuilt alternator?
 

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at idle your alt. should be putting out about 14 volts...to your bat... if you don't have 14vdc when idling, you are not charging....something is wrong. My guess, unless the belt is squeeling like hell or not there, its time for an alternator
 

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My 04 V8 has never displayed 14V on the gauge. My experience is that somewhere in late 04 or early 05 Volkswagen changed the operation of the gauge to display a steady 14V when it's charging somewhere between 13.5-14.2V and only reads less when it's not charging but the early models actually seem to read more accurately i.e. The gauge moves up when revving. And only reads 13.5-13.8V normally. To know if you have a bad alternator you need to measure the voltage output at the alternator while it's running and compare that to the voltage reading on the cluster. If you have ~14V at the alternator but the gauge shows 12v then you have a voltage drop somewhere, most likely not your alternator cable if you say it's new. I'd check the ground point on the right frame rail near where the alternator sits, it has a large castle nut on it. If there is only 12V at the alternator then you've got a problem there. That's my 2 cents.
 

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I'm not sure you are totally right about the gauge.

My 2003 reads just over 14V in steady state when running and 14.5V when first started and the alternator is catching up.
 

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I had the same problem with my 2004 V8. I took it to the dealer and they said there was a TSB concerning the problem. It was a faulty cable that runs from the battery to the alternator. Check it out.
 

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I could be off on which 'regs read constant 14V but my point was some early '04 V8's in the U.S. read less than that and are running normally.
@Perry01 -Treetz said he'd already had the cable replaced.
 

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Discussion Starter · #7 ·
Today it started right up and stayed around 13.5-almost14V even at idle. Puzzling. I put the battery on charge all day and will have to employ VAGCOM to look at the voltages as well as check out the grounding points. It is possible that the front ash tray being left open for four days drained the battery via the illuminated red ring I suppose as I'm not sure if it shuts off by itself. This was the first electrical trouble I have experienced since replacing the B+ alternator/starter cable, but I've always had bad KESSY mosfets and resistors in the back of my mind since reading about voltage leaks there. This was also the first time I've seen the voltmeter drop so low since replacing the cable... used to see it all the time before replacing it. Thanks for the suggestions and insight from everyone.
 

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Experiencing same fluctuating volt meter at idling on my 2004 V8.
Brought my 2 years Battery at Autozone for check they said it's ok.
I will check voltage levels at alternator versus battery and also this cable referenced in the TSB, this could be the root cause. Hope alternator is OK, this is a pure nightmare to replace it.
 

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I finally did the cable a few weeks back. Had one issue where cluster was dim and voltage needle was dead.....but it still started strong and it fixed itself a few hours later? I was thinking that the bogus B+ cable made my alternator work harder and therefore, shorten its life? I had my keyless entry working for a few hours and then went dead. It was nice to have but I give up..
 

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Well, my 2004 V10 is home after a costly generator replacement and hell yeah, it solved the needle oscillation issue. Mine was dancing from 14 to 13.5V most of the time since last summer. My mechanics also replaced the rubber drivebelt, cooling hoses + fittings and the cable from the generator. A little sidenote: the engine runs more smoothly.
 
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