Changed it for another OEM Bosch new (not reman). Subsequent test showed it was now good.
Update: There was a direct short in the alternator and when it shorted internally it also took out the 200 amp protection fuse ($115) too for the battery. I got a new Bosch unit and I was happy to find out I did not have to bring it to the nearest dealership and that a local German repair shop were able to do it.
First, if your alternator is putting out 13.8V while the car is running, your alternator is fine. Period. If your battery passes a load test after being fully charged, it is fine.
I replaced it with a Duralast Gold. After replacing the issue still existed so I replaced the alternator with an OEM Bosch remanufactured unit.
New Bosch installed Thanks for your help. It was in fact the alternator. Had a NEW Bosch installed by M&M Auto/Cycle in Jersey . Mikes the man when it comes to TDI service.
I had a Valeo alternator from an 03 Jetta in my garage, so I slapped that in and made the connector work somehow. Its working perfect now. 14.5v almost instantly at startup. Weather is below 30F.
Im having the same issue with my 08 jetta 2.5, replaced the alternator and voltage regulator because the car battery wasnt charging anymore. Anyways replaced the alternator and then I had a high voltage issue with the regulator
Alternators don't make good battery chargers and if your alternator is on its way out then it may not be able to charge the battery. A fully charged battery measures 12.6V when the car is not started. When it's discharged by 75% then it measures 12.4V. if it's like 12V then it's totally dead. When you start the engine and the alternator turns, at idle you should have at least 13.4 Volts. If it's less than this then try reving the RPM's to like 2000rpm. You now should have at least 13.4V. If you don't then you have a problem either with the regulator or you have a bad diode.
What bugs me now is that it seems the alt doesn't quite put out. Dash light (at least the one I put under the dash since the one in-dash quit working) won't go out. Goes from bright to dim when the alt should excite.
A friend had a rebuilt bosch unit that he lent me to try and that too doesn't put out any voltage.
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