Massive battery drain (!)

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bhodgkiss

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Hi All,

Hoping you can help!

B8 3.0tdi avant

The battery recently died (was old) so I replaced with a nice new Varta 110Ah last week

A week later it’s flat and showed 11.1v yesterday.
So I charged yesterday and got it up to 12.5v by end of day, and locked it last night
This morning it was down at 11.6v

I got my multimeter on the 10A setting and connected it in series with the battery terminal and negative lead..... expecting 3A if it’s draining somehow.... and it whizzed up to 13A and blew the multimeter fuse!!!

so have ordered a new fuse....

what could be drawing this much current please? When I reconnect the negative battery lead there’s a great big spark

- I installed the new battery properly and have driven it since

- what would cause such a big current draw?

I fitted a cheap Chinese front passenger door lock mechanism last week, which works fine, and when I disconnected the main door connector to isolate it, I got the same big current draw, so I don’t believe it’s that.

So I guess I now try and locate the large current via the fuse box, but may blow the multimeter fuse again?

many thanks
 
Did you code the new battery in with VCDS? If not this may be your issue.

If there is a current drawing power from the battery when it shouldn't be the ECU will recognise this and log it as a fault as quiescent current.

When you first connect the battery up I wouldn't be surprised if that amount of power is drawn with all the modules, ECU, BCM waking up, glow plugs possibly coming on etc.

If it was me I'd plug it in and scan for faults first and see if that fault comes up.

Chances are there will be loads of random non related coded just because the battery is so low.

I'd clear the codes, code the battery in and give it a good charge with the terminals up front in the scuttle panel.

Take it for a drive.

Scan and clear codes and take it from there.

If it's still drains the battery after all that I'd scan again for faults and see what it throws up.

Failing that your going to have to remove a relay/fuse at a time to see what is draining the battery.

Sent from my moto e5 plus using Tapatalk
 
Like @jakm15 says you will need to code the battery in with VCDS. With the current draw the way to get a true reading is to wire the meter in series like you have. Once that's done you need to close all doors, boot and bonnet (with the meter where you can see it) and lock the car. once the car has settled down and gone to sleep that's when you will be able to see what the current draw is. With the car unlocked all the modules are awake so the draw will be quite high.
 
Strange if an Audi B8 is different, but I have messed about looking for current drains on a late 2009 Ibiza SC and checked it against a 2015 Polo and neither needed the doors locked to allow the car controllers to be put to sleep, all that was needed was maybe 20 minutes, though maybe these B8's are down to 10 minutes before the controller have switched off all "not needed" power demands. Even with the bonnet open and unlocked they both went to sleep quite quickly.

This sounds like a wiring fault or a component fault, in a B8 I'd be looking at removing the main power feed to each of the many power distribution areas or fuse boxes one at a time and playing safe initially and just connecting the multimeter across the battery as when you remove loads the voltage will rise and much safer way initially than trashing your multimeter.
 
rum4mo said:
Strange if an Audi B8 is different, but I have messed about looking for current drains on a late 2009 Ibiza SC and checked it against a 2015 Polo and neither needed the doors locked to allow the car controllers to be put to sleep, all that was needed was maybe 20 minutes, though maybe these B8's are down to 10 minutes before the controller have switched off all "not needed" power demands. Even with the bonnet open and unlocked they both went to sleep quite quickly.
Click to expand...

I haven't actually tried it on the B8. That is just from my experience working on Ford and Volvo in the dealerships. The method I mentioned was used stated in the technical manuals for those.
 
things like the audio system, seat sensors and all sorts stay on in the Audi until it is happy that it is locked and you have walked away. Until that point it is staying in "ready mode" for you to use available functions.
 
Simon said:
things like the audio system, seat sensors and all sorts stay on in the Audi until it is happy that it is locked and you have walked away. Until that point it is staying in "ready mode" for you to use available functions.
Click to expand...

I'd think that if you wanted to test this, you could leave a window and the car unlocked and you would find that everything would still go to sleep in the same time - even leaving a door open after a certain time the interior lights would go off as the car went to sleep.
 
Many thanks all

I’ll give it a go

How many amps does everyone else see when connecting a multimeter in series with the battery please?
 
You'll need to measure the true idle current with a fuse removed and repeat for all fuses. Since the multimeter fuse blew then the car is turning on high loads - the obvious thing which comes to mind are the lights - is it set for auto? You'll need to stop that large current before you can diagnose. 13+A is not your problem because that would kill a 110Ah battery in less than 12 hours.

I haven't done any measurements on my B8, but I had a problem on my B5 which I diagnosed with the fuse removal method. Before the interior lights went out it was about 3.5A. Then it would be about 0.33A for 5 minutes before dropping to 0.08A. In my case my battery was being drained in 1-2 weeks so I correctly guessed that my car had a problem where sometimes it would stay at 0.33A, and it turned out to be an issue in the audio entertainment equipment, which was taking the bulk of that 0.33A before it went to sleep (and of course sometimes it wouldn't).

If your 110Ah battery is draining from 12.5V to 11.6 V in about 12 hours then I guess your drain is in the order of several amps. That's something major, along the lines of a fan or pump running permanently (although I assume that you're not hearing anything?)
 
bhodgkiss said:
Many thanks all

I’ll give it a go

How many amps does everyone else see when connecting a multimeter in series with the battery please?
Click to expand...

Initially the aim was somewhere around 50 milliamps, though probably less than 100 milliamps would be okay but not as per intended spec.

How I would always measure drain current once getting it down to "safe" levels, is to use a multimeter with a 20 amp DC range and connect one side of it set in 20 amp current range, to the local earth bonding stud beside the battery -VE post, then, after the car's controllers have gone to sleep, ie wait 20 minutes, place the other multimeter lead, which must be slim enough for the battery -VE clamp to lift off over, firmly down onto the battery -VE post top, then slacken off and lift off over the multimeter probe, the battery -VE lead, by doing that you have made sure that you are not going to cause the car's controllers to re-awaken and so the meter will truly read the "sleeping" drain current". Though you need to be able to witness that battery voltage risng a bit while the controllers are still awake by removing fuses, before trying to blow your next multimeter fuse. I'm lucky as I managed to justify to myself buying a quality and so trusty AC/DC current clamp, so I have no excuse of ending up diving in and blowing any of my multimeter's fuses - or worse.
 
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Many thanks

I’ve now recoded the battery, incrementing the serial number by one digit in the middle
Here are groups 18-20 in VCDS, battery current says up to 27A in group 18? (18A below but this keeps creeping up as engine idles)



Any thoughts on this and what’s normal please? Sounds really high to me!!! Engine is just idling, lights off, bonnet, boot and door open

Aside, when running the engine fault scan it is saying ‘Relay for supply voltage Terminal 30 (J317) implausible signal’

anything juicy?
 
Last edited:
Sorry no idea but these battery stats look horrible 23AH !

Edit:- my only way of sorting that out is to locate the areas that are causing the high current draw, maybe not simple/quick just a lot of disconnecting certain areas to dig down towards where the high current draw is going.

Another edit:- the thing remember is, most of all power users get switched/connected to their user via a controller, when you are investigating high current draw, you might disable a controller and find the current high current draw has gone, but you would then have to find out which users are being switched by that controller so reconnect that controller and start disconnecting its users/switched loads - that all takes time - there again, it might just be a trapped wire/wires.

Not rocket science but not pi** easy to guide you into remotely.
 
Last edited:
Many thanks
So I start with the main connections under the bonnet (at the back in the centre) next to battery + post? Alternator etc to disconnect and then try?
 
I'd stick the battery on charge overnight with the terminals under the bonnet and take it from there as it may just be a case of you needed to code it.

9 times out of 10 it's usually the easiest and simplest solution that works so I'd start with that if I was you, it might be right now.

Sent from my moto e5 plus using Tapatalk
 
bhodgkiss said:
Many thanks
So I start with the main connections under the bonnet (at the back in the centre) next to battery + post? Alternator etc to disconnect and then try?
Click to expand...

I don't think that you should go into this blind, maybe buy a Haynes repair manual as support or buy a manual from somewhere like easymanuals or Erwin.

Edit:- though now that you have mentioned it, you could disconnect the main output from the alternator to dismiss it first of all.
 
Hi All

Just to update on this:

Many thanks to Karl on here for his help as always

So I found that the 30A fuse in the RH boot compartment was showing 0.6mV with the car in sleep mode, so drawing around 0.4A constantly

This is linked to the B&O amp in the left hand boot compartment
Water has obviously got to it at some point, as it's been repaired before (I found a sticker on it)

So pulled the fuse for now but I need a replacement amp - pricey even second hand!

I believe the water leak is now fixed from the sunroof.
 
I believe the biggest killers of B&O amps in sedans is water leaks from the boot lid. Water getting in through the light seals. When the boot is opened the water goes down the boot supports and drenches the amp. I'll be listing some parts in the classifieds in a few weeks and I've got a 8T0 035 223 AN. Not sure if that's the one you need?
 
Many thanks
The amp is now being repaired and I’ll get a water cover for it (and hopefully fix the leak!)
Mine part number has ‘T’ on the end
 
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