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Alternator problem ?


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I suspect my alternator might be on the way out on my 2003 996 TT.

Engine cranked fine and fast but on the drive home I noticed the battery voltage on the dash was less than 12V, so when I got home I double checked with my digital voltmeter and yep it was low.

I turned on the headlights to see what would happen but they struggled to ignite and the battery voltage stayed <12V.

Revving the engine had no effect on battery terminal voltage.

No warning lights on the dashboard.

I replaced the battery a few months back as the OEM gave out.


Are there any codes I could pull to determine the alternator charging current or lack thereof ?

How difficult is an alternator DIY ? Edit - just found a DIY on 6speed - looks pretty straight forward.

Looks like I might be getting my hands dirty again after just replacing the spark plugs and coils :-)

One last observation - I did notice that after a restart for a few seconds the battery voltage went up to just under 14V then settled back down to under 12V. Not sure if this tells me the alternator started to charge then gave out.

Might have the battery tested at where I bought it from just in case it's failed - unlikely.

Thanks again guys, Tim

Edited by timf
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I agree / hope :-) it seems to start to charge then after about 5-10 seconds voltage drops from 13.8V down to less than 12V - revving the engine has no effect.

Doesn't look to hard to get to the alternator, plus by trade I'm an electronics engineer so fairly confident I could perform the electrical repair (rectifier bridge would be my first guess).

Time for a bit more googling me thinks !

EDIT - seems it could be the alternator clutch pulley which has failed, hmmmm


Sounds like the regulator on the alternator.

I've seen a DIY on replacing the component rather than the alternator, a big saving.

Edited by timf
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Thanks for the link - seems to be quite a bit of info on the web about this.

As an EE I was originally trained in military aircraft Avionics, then moved onto telecomms, then Formula 1 / CART engine management for Cosworth then back to Telecomms (mobile phones) for Qualcomm and Motorola - so I've had a pretty interesting career :-)


Here you go, good luck


What kind of electronics you work with?

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