Battery drain - Fuses 36 and 42

I have known alternators to look like they are charging correctly but still be faulty.
Is there a way of testing the alternator? It always seems fine when the car is at rest, but after a drive the battery can actually lose voltage.
 
You could drive the car with VCDS connected and log the alternator output voltage. Just make sure the cable is routed away from the pedals and controls. Mac could then monitor the readings.
 
You could drive the car with VCDS connected and log the alternator output voltage. Just make sure the cable is routed away from the pedals and controls. Mac could then monitor the readings.
Is that groups 18, 19, & 20?
Screenshot_20230301-202758.png

Mac.
 
Those would work. While on the drive you may look around to see if any other measuring blocks are fluctuating. The log function is ideal for data logging on the run.
 
Hi all, I think I've found the main culprit of this problem!

After going away for a week, and leaving the battery disconnected, when I got back the battery had lost barely any charge - so battery seems fine.

I reconnected the battery and locked the car as normal, and the battery lost around 0.07v per day - so something is definitely drawing power when it shouldn't be.

As recommended as the next step/test here, I disconnected the heater/ac unit (not sure on the correct term), left the battery connected and locked the car and the battery is still holding virtually all of its charge!

It seems this unit has already been replaced before, so do I write this one off and source another replacement? If so, has anyone got one I can buy please?!

20230316_134006~2.jpg

20230316_133942~2.jpg


20230316_133956~2.jpg
 
Hi all, I think I've found the main culprit of this problem!

After going away for a week, and leaving the battery disconnected, when I got back the battery had lost barely any charge - so battery seems fine.

I reconnected the battery and locked the car as normal, and the battery lost around 0.07v per day - so something is definitely drawing power when it shouldn't be.

As recommended as the next step/test here, I disconnected the heater/ac unit (not sure on the correct term), left the battery connected and locked the car and the battery is still holding virtually all of its charge!

It seems this unit has already been replaced before, so do I write this one off and source another replacement? If so, has anyone got one I can buy please?!

View attachment 105801
View attachment 105802

View attachment 105803
That matches the "too many errors" in the Climate Controller, in the scan.
Pop a wanted ad in the Market Place. Meanwhile see you tomorrow!
Mac.
 
Hi all, I think I've found the main culprit of this problem!

After going away for a week, and leaving the battery disconnected, when I got back the battery had lost barely any charge - so battery seems fine.

I reconnected the battery and locked the car as normal, and the battery lost around 0.07v per day - so something is definitely drawing power when it shouldn't be.

As recommended as the next step/test here, I disconnected the heater/ac unit (not sure on the correct term), left the battery connected and locked the car and the battery is still holding virtually all of its charge!

It seems this unit has already been replaced before, so do I write this one off and source another replacement? If so, has anyone got one I can buy please?!

View attachment 105801
View attachment 105802

View attachment 105803
Good Evening,

If you do replace the climate panel you can reuse the front panel, it is in excellent condition, so don't be put off buying a replacement climate that looks cosmetically worn.

Andy

Andy
 
Right. The saga continues...

For whatever reason, having been absolutely sure when I plugged in the replacement unit the battery was no longer draining, after switching the fascia/buttons over it now just drains exactly the same as the original unit...

I've gone through a laborious process of connecting/disconnecting each unit, and even thought I'd narrowed it down to the red/white cable that goes to it (which apparently does nothing as it functions without it plugged in?) - but it doesn't seem to matter what's connected or disconnected anymore, the battery drain is now constant (even with no unit connected - which entirely stopped the drain when I first tried it weeks ago...).

Here's my daily log of what I've tried. This is me unlocking the car, opening the boot, and taking a simple volt reading across the battery terminals to see what's happened in a day:

NEW UNIT
22nd March - 12.42v Plugged in new AC loose (not fully pushed into console)
23rd March - 12.40v Stable
24th March - 12.40v Stable. Switched AC fascia/buttons + installed fully
25th March - 12.33v (-0.07) Why?!
26th March - 12.25v (-0.08) Pulled unit out but left connected (incase pushing it into console did something)
27th March - 12.18v (-0.07)
28th March - 12.11v (-0.07) Disconnected red+white cable
29th March - 12.16v (+0.05) ? Wtf...
30th March - 12.20v (+0.04) ? Plugged original unit in including red+white cable

OLD UNIT
31st March - 12.06v (-0.14) Disconnected red+white cable
(- 12.70v after 30 min drive)
(- 12.40v after 7 hours)
-----
1st April - 12.42v Charged after drive home and left overnight
2nd April - 12.30v (-0.08)
3rd April - 12.23v (-0.07) Disconnected all

NONE
4th April - 12.16v (-0.07) Wtf.


Mac is kindly going to scan it again this weekend to see what codes might come up. But other than that I'm at a total loss with this again...

What else could've happened/changed since the first time I unplugged the unit (which stopped any drain completely)?

Anything else to try?! I know this unit is somehow linked to the alarm/interior sensor, but I unplugged that switch previously and it made no difference.

Anyone know an auto electrician?!
 
Last edited:
Right. The saga continues...

For whatever reason, having been absolutely sure when I plugged in the replacement unit the battery was no longer draining, after switching the fascia/buttons over it now just drains exactly the same as the original unit...

I've gone through a laborious process of connecting/disconnecting each unit, and even thought I'd narrowed it down to the red/white cable that goes to it (which apparently does nothing as it functions without it plugged in?) - but it doesn't seem to matter what's connected or disconnected anymore, the battery drain is now constant (even with no unit connected - which entirely stopped the drain when I first tried it weeks ago...).

Here's my daily log of what I've tried. This is me unlocking the car, opening the boot, and taking a simple volt reading across the battery terminals to see what's happened in a day:

NEW UNIT
22nd March - 12.42v Plugged in new AC loose (not fully pushed into console)
23rd March - 12.40v Stable
24th March - 12.40v Stable. Switched AC fascia/buttons + installed fully
25th March - 12.33v (-0.07) Why?!
26th March - 12.25v (-0.08) Pulled unit out but left connected (incase pushing it into console did something)
27th March - 12.18v (-0.07)
28th March - 12.11v (-0.07) Disconnected red+white cable
29th March - 12.16v (+0.05) ? Wtf...
30th March - 12.20v (+0.04) ? Plugged original unit in including red+white cable

OLD UNIT
31st March - 12.06v (-0.14) Disconnected red+white cable
(- 12.70v after 30 min drive)
(- 12.40v after 7 hours)
-----
1st April - 12.42v Charged after drive home and left overnight
2nd April - 12.30v (-0.08)
3rd April - 12.23v (-0.07) Disconnected all

NONE
4th April - 12.16v (-0.07) Wtf.


Mac is kindly going to scan it again this weekend to see what codes might come up. But other than that I'm at a total loss with this again...

What else could've happened/changed since the first time I unplugged the unit (which stopped any drain completely)?

Anything else to try?! I know this unit is somehow linked to the alarm/interior sensor, but I unplugged that switch previously and it made no difference.

Anyone know an auto electrician?!
Just a thought, maybe swap the facia back to the to the one that came with the replacement Climate Controller?
See you over the weekend. If you want to borrow the clamp meter, pop round.
Mac.
 
Final update, because I'm just absolutely stumped by whatever this issue is/was and give up...

Tried 2 different multimeters testing current today, Mac's proper Fluke clamp version, and my own cheap version - both reading 0.0 or 0.01 respectively, regardless of which AC unit was connected.

20230407_151519.jpg


20230407_154806.jpg


So, apparently there's no more drain, even though nothing has actually changed and the battery is losing on average a steady 0.07v a day.

Absolutely no idea why the car has failed to start multiple times over the last few months, as the battery itself holds charge perfectly, and the alternator appears to be charging it...

Good luck to anyone that ends up here with a similar issue!
 
Final update, because I'm just absolutely stumped by whatever this issue is/was and give up...

Tried 2 different multimeters testing current today, Mac's proper Fluke clamp version, and my own cheap version - both reading 0.0 or 0.01 respectively, regardless of which AC unit was connected.

View attachment 106682

View attachment 106683

So, apparently there's no more drain, even though nothing has actually changed and the battery is losing on average a steady 0.07v a day.

Absolutely no idea why the car has failed to start multiple times over the last few months, as the battery itself holds charge perfectly, and the alternator appears to be charging it...

Good luck to anyone that ends up here with a similar issue!
I wouldn't worry about the 0.7 volts drop. Because there are components that, although they go into standby mode, will draw a small current, and the battery voltage will reflect that.
As long as the battery sits at 12.5 to 12.8 volts with the engine off, I'd be happy.
We checked the alternator voltage and charging current last time, so again, no worries there.
Check the battery voltage just before you do the first start of each day, and make a note of it.
🤞Mac.
 
Have known alternators to "function" correctly yet when the engine not running drain the battery down. Hence the suggestion to try a different alternator.
 
You may have a good point there Graham, one of my Fsi's had the battery light on, replaced the alternator ( Used ) battery light now has gone out, but 1/2 an hour after running the car the battery goes flat,
 
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