Mgmike1

Hi.
I have 3 Litre TDI Quattro. 2008 in UK
Replaced battery with new one from Halfords last year as it failed to start one morning
It used to show battery level dropping over several days on the MMI but now shows 100% even when it's flat and won't turn over to start. Sometimes takes a week to drain so what's likely to be causing the drain as surely immobiliser won't do that quick?
Third party garage says alternator is ok. Has to use a power pack on remote terminals under bonnet and that started ok but started showing 100% charge after that.
Any ideas please as charged the battery overnight and it shows over 12 V now but will drop with whatever is draining over the next few days.
I haven't any extras that are fitted so that's not an issue
Many thanks in anticipation
Mike

Giovanni Giovino 6.0+6.0TT

You are in the A8/S8 forum, NOT A3.... Post your question in A3 forum.

Jack88

He never specified A3, which isn't even available with the V6 TDI.

Jack88

The battery level indicator is pretty useless, so I wouldn't take much stock in it. There are a few potential causes, but there have been a number of threads on the subject here before. It's not likely a problem specific to your engine. Here's a couple threads on it;

battery discharge overnight
MMI problems and dead battery

Giovanni Giovino 6.0+6.0TT

Hello Jack,


My mistake, I mistook the title "Audi 3" for A3, and being he was in the UK, and a A3 S-Line came with a 3.0 or 3.2, but again I may be incorrect on that....

Jack88

No worries, it's easy to misunderstand, it wasn't written clearly. If I recall, the A3 could be had with the gas V6, but only the 4 cylinder diesel.

MP4.2+6.0

Search in general. Too wide open a field of possibles. First step I would say is you need a good scan. Not just the ECU with the generic scan tools, but all modules--like VCDS or the dealer equivalent.

You could have variously one of several tuners, or the car alarm w/ built in battery (factory set up), or a variety of other things that are sucking power when car is off and not shutting down/working properly. Scan may give you better pointers of what are showing errors or issues. You will have lots of power management codes as a given BTW. But those are just symptoms, not the what the issue causing the problem actually is.

Mister Bally

Regardless of 3rd party garage saying alternator OK, search for posts by me on battery drain issues. You describe the classic leaky diode that latches in a shorted state which drains the battery in less than eight hours. Once drained and recharged, the alternator is fine for several days, then when you need the car most, BAM! dead battery.

I describe to to troubleshoot this issue in several earlier posts. You the advanced search function to find posts by me in related threads.