Question about 2000 Audi A4

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Battery indicator after new alternator Audi A4

2000 Audi A4 1.8
Battery indicator came on and voltage dropped to 10V. AAA tech used portabel diagnostic indicator and determined alternator was bad. Car did run with a jump although at 10V. Towed to AAA certified mechanic. They replaced alternator. Voltage back at 14V for a few miles then battery indicator came back on. Voltage now at 12V. Do I need a battery? Is there a voltage regulator in the Audi? Could it be the alternator was not bad after all? I just want some knowledge before I talk to the mechanic about it.

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  • pdu111 Jul 02, 2009

    I believe the alternator was a high quality remanufactured unit. Cost me about $490 for the part. I just talked to an Audi service person who said they dont see many alternators or voltage regualators go bad but batteries are usually the culprit.

  • pdu111 Jul 02, 2009

    Its a Bosch alternator $490. The battery has a date of 2004. How many years should the battery last?

  • yadayada
    yadayada May 11, 2010

    anything is possible, was a new alt used or a rebuilt? have the system retested

  • Gervacio Magalong
    Gervacio Magalong Aug 16, 2016

    I am having this same problem. Old alternator died and was reading 8v at the battery.

    Installed new one from advanced auto, read 14v after install. After about 25 miles it now reads 12v when running and not charging.

    How did you fix your issue?

  • Gervacio Magalong
    Gervacio Magalong Aug 16, 2016

    I am having the same problem. Old alternator when running tested at 8v so I replaced it with one from advanced auto. Measured 14v and charging after install. 25 miles later it now reads 12v and is not charging the battery. I have replaced both grounds (one up top and the other from engine block to body) still reading 12v

    I am desperate. How did you fix yours, I dont want to shell out $600 for one from Audi only ot be in the same spot!



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Check the little wire that attaches to the back of the alternator it could be broke or hooked up wrong the wire should be connected to the passenger side prong

Posted on Nov 22, 2016

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Take it to an Audi dealer. Could have been a bad alternator, and another bad alternator if they didn't use Audi part. Don't use cheap rebuilt Chinease stuff on your Audi.

Posted on Jul 02, 2009


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The alternator charge rate is regulated by a voltage regulator. Because the alternator output is connected to the battery, the alternator and battery voltage will be the same and the voltage regulator monitors that voltage.

The lower the battery voltage the more output the alternator will produce in order to correct the situation but because a lead acid battery has a high internal resistance to accepting a charge the terminal voltage will quickly rise to the alternator regulated voltage and fool the alternator into thinking the battery is fully charged when the output will drop to the order of just a couple of amps.

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