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Discussion Starter · #1 · (Edited)
Hi all,
Help please.
Quick background, had this exact issue about 8 or so weeks ago, got it to a garage, fault wasn't present when they started the car, ran various tests on the battery and alternator and couldn’t find a fault. Cars been fine ever since. Indeed when I had got it back, it’s been fine.

ffwd to now, and the issue is back. I have a glaring warning appear after about 3-5mins of starting the car in the screen between the speedos “ alternator fault: battery is not charging”. Ignore it and start the car a few times and you’ll find the battery dead.

Charge the battery with a trickle charger, registers full, I leave it overnight and re attach the charger next day, confirms still full. Start the car, fault returns and can’t clear the codes (DTC power management codes throughout - so limited fan function, can’t heat rear screen or use seat heaters etc).

Most garages can’t seem to fit me in until next week, and it doesn’t give much confidence thinking you can pop to the supermarket only to find your car dead on return.

As the alternator was tested before and couldn’t find an issue.. I’d be surprised if it was at fault.. but regardless is there any way I can test things to isolate if this is a battery or alternator issue? Instinctively I’d like to just replace the battery but at £150-200 a pop, don’t want to do this to find it’s wasted money (side note, my current battery is an AGM 12V 105ah 950A varta, should I match this like for like? My car doesn’t have stop start (at least enabled), searches suggest thats what this battery is good for, and registration searches give you wildly variable batteries based on registration - how do I know which would best do the job?).

Between my trickle charger and code reader thing I can already say the following;

-On testing this morning from leaving the battery full last night, the charger registered 12.9v on connection before charging started again.
-With the car running, my code scanner registers via ODB port between 11.36 to 11.19v while running.
-on charge it registers c13.4v / 10.1A

..what else do I need to test to help identify what could be at fault?

Thanks
 

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What are the codes? The car is not charging but if could be either the alternator or the battery management electronics.
It would seem that the battery is generally OK, however if it has been deep discharged then this can cause internal damage.
 

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Discussion Starter · #3 ·
What are the codes? The car is not charging but if could be either the alternator or the battery management electronics.
It would seem that the battery is generally OK, however if it has been deep discharged then this can cause internal damage.
Hi,
Main ones is;
U100800 “Active / Passive: Diagnostic Interface for Data Bus - Read out DTC”

Then related ones are
-03041 Energy management active

-00457 Check DTC memory - vehicle Electrical system control module

-00457 no signal / communication - vehicle Electrical system control module

-02252 Electrical fault in generator

the battery was so flat the car wouldn’t start
 

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Hi,
Main ones is;
U100800 “Active / Passive: Diagnostic Interface for Data Bus - Read out DTC”

Then related ones are
-03041 Energy management active

-00457 Check DTC memory - vehicle Electrical system control module

-00457 no signal / communication - vehicle Electrical system control module

-02252 Electrical fault in generator

the battery was so flat the car wouldn’t start
I had this on my previous 3.0 TDI A5, never really got to the bottom of it before the car was written off by the actions of a blind old fool :(

Mine would happen within a few seconds of starting......where the revs would hover around 900 or so then usually drop down to the 650 rpm idle, but instead the error message would pop up & the revs would rise to around 1000rpm & stay there.
When it first happend there was slight thud from the front of the car, although nothing was visually wrong with the alternator, no burn marks & the pulley was free etc.
Turning off & on didn't solve the issue & there was a raft of DTC's similar to what you have & clearing them wouldn't solve anything.
Changing the battery helped for a month or so but it then came back occasionally, but would clear if I tunred the car off & on again.
Monitoring through VCDS showed that the alternator was indeed working & charging the battery as it should.
I figured that it might be the regulator that was playing up & not energising the alternator as I found that if I raised the revs after starting the engine to around 1200rpm or so for a few secs it would be fine.
I did come across a few posts (on FB I think) where people had had similar issues & it turned out to be either the regulator had been failing or the brushes were shot in the alternator. Most people changed the alternator but some changed the regulator &/or brushes, which I believe are accesible without taking the alternator off.
 
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Hi,
Main ones is;
U100800 “Active / Passive: Diagnostic Interface for Data Bus - Read out DTC”

Then related ones are
-03041 Energy management active

-00457 Check DTC memory - vehicle Electrical system control module

-00457 no signal / communication - vehicle Electrical system control module

-02252 Electrical fault in generator

the battery was so flat the car wouldn’t start
03041 just means the battery was low so the system needed to take action, and 02252 means that it detected that there was no charging. The ones that are of concern are 00457 because they indicate that a control module is not communicating. Based on this I'd suggest that there is no problem with the alternator and its more likely a battery management unit issue.
 
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