Charging Alternator Issue..Need Master Advice
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AudiWorld Member
Joined: Jan 2011
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From: Southeastern Wisconsin
Charging Alternator Issue..Need Master Advice
I am not completely sure if my alternator is bad or if I just have a bad newer battery. The voltage at the battery terminals while running reads 13.00-13.4 it normally reads only 13.1 depending on how long it runs. Does anyone know how the charging system works on the car, because my vag-com shows no faults and all is ok with the charging system, but after a few starts or leaving anything on for a little while the battery is dead. I will have the battery replaced, but I would like to know what the voltage should be normally. Thanks
AudiWorld Super User
Joined: Sep 2010
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From: New England
You should have ~14V at the battery terminals with the car running. Check belt tension. If tension is ok your alternator is going bad as 13.4V is too low.
I am not completely sure if my alternator is bad or if I just have a bad newer battery. The voltage at the battery terminals while running reads 13.00-13.4 it normally reads only 13.1 depending on how long it runs. Does anyone know how the charging system works on the car, because my vag-com shows no faults and all is ok with the charging system, but after a few starts or leaving anything on for a little while the battery is dead. I will have the battery replaced, but I would like to know what the voltage should be normally. Thanks
AudiWorld Senior Member
Joined: Oct 2005
Posts: 643
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From: sunny florida
what year is the AUDI?,no joe blow can replaced that batt,the AUDI has a
batt management sys in it,vag it in eng and ck channel #4 to see what the
alt is putting out,rev engine with the lites on and ck output,13.50 and
higher alt is good,heat will kill a batt and age,
hope that helps,
DAN B.
batt management sys in it,vag it in eng and ck channel #4 to see what the
alt is putting out,rev engine with the lites on and ck output,13.50 and
higher alt is good,heat will kill a batt and age,
hope that helps,
DAN B.
AudiWorld Super User
Joined: Nov 2010
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From: Vancouver, Canada
Measure the voltage on the battery management unit not on the battery directly (opposite end). It should be 14+V when engine is running and less when it is off. How much lower it depends on your battery. If it is close to 12V battery is not good anymore, but even if it is higher it is steel not proof that battery is good. It can keep voltage but loose capacity. You can also recharge your battery and then try those few starts. I think it is battery. Alternator would work or not and you would have warning if it is not working. It won't just lower the voltage.
AudiWorld Super User
Joined: Sep 2010
Posts: 3,061
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From: New England
Battery capacity (vs. instantaneous voltage) is an important consideration, but if the alternator is putting out less than 14v it's largely a moot point.
Of course it's easier to first substitute a known good battery and then see if it loses charge, again provided you're assured the alternator is ok.
Of course it's easier to first substitute a known good battery and then see if it loses charge, again provided you're assured the alternator is ok.
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Joined: May 2003
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Alternator
I try installing a good healthy battery first to properly test the alternator.
when you get the reading, is it with light on, a/c on?
13.4 and above with the alternator you have is ok with the lights and a/c on at idle.
the alternator you have is a water cooled Hitachi with an output of 190 amps, I have not replace one in an A8 yet.
when you get the reading, is it with light on, a/c on?
13.4 and above with the alternator you have is ok with the lights and a/c on at idle.
the alternator you have is a water cooled Hitachi with an output of 190 amps, I have not replace one in an A8 yet.
AudiWorld Super User
Joined: Jan 2006
Posts: 6,310
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From: Las Vegas, Nevada USA
I try installing a good healthy battery first to properly test the alternator.
when you get the reading, is it with light on, a/c on?
13.4 and above with the alternator you have is ok with the lights and a/c on at idle.
the alternator you have is a water cooled Hitachi with an output of 190 amps, I have not replace one in an A8 yet.
when you get the reading, is it with light on, a/c on?
13.4 and above with the alternator you have is ok with the lights and a/c on at idle.
the alternator you have is a water cooled Hitachi with an output of 190 amps, I have not replace one in an A8 yet.
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AudiWorld Super User
Joined: May 2003
Posts: 2,729
Likes: 6
Mileage
have seen 4-5 with 140k, mostly in the lower range 40-80
never replace an alternator on the A8s yet.
may have to do with the battery management unit in the Touareg/Q7/Cayenne, on which I seen more than a few failures.
never replace an alternator on the A8s yet.
may have to do with the battery management unit in the Touareg/Q7/Cayenne, on which I seen more than a few failures.
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