Electrical/battery drain issue

John L

A2OC Donor
I have been having an issue for quite some time now with the car running out of battery if it is left for more than a week or so.
Removing fuses 36, 42 and 39 (central locking, other central locking and right hand doors) before parking seems to resolve the issue.
Sometimes there is a slightly odd noise to the right hand door looks when locking or locking (kind of delayed response but a bit louder than the left hand side).

The car is a European spec 1.2tdi with aircon and original hifi. The hifi has a blaupunkt bluetooth adaptor attached but this seems irrelevant given that its fuse was not removed.

The car also has Osram light@day fog/daytime running LED lights fitted and interior led bulbs from hypercolor (the German supplier of A2 interior light kits).
One of the map reading lamp LED bulbs was at one stage faulty with a break/crack in the solder to one pole. I resoldered it and have had no issues since. I noticed then, even though not lit, it was very warm (the switch to it was on).
None of the other lights have been warm when I have checked.


The problem I guess began after the led lights were fitted (but these do not light when the car is locked and so should presumably not be drawing so much current).

I have experienced an odd issue with the Osram lights. This is that when the car is plugged into a mains charger the Osram lights blink. I have no idea how they are wired but think I found out today. There is a red cable that is bolted in to the floor in the electronics bay under the drivers floor. As removing fuses before did not seem to disable the Osram lights from flashing I guess they must take their power from here. This could be to overcome the issue of Ecomode disabling the DRL's as it shuts down the engine.

Please advise a better solution if you have any ideas so that I can try to wire the lights in a better way.

The DRL blinking does not occur when a booster battery is connected or at al during normal operation.

The CCU is made by Temic and has the part number: 8Z0 959 433 M Zentrale Komfortelektronik.

Does anyone know if this version is prone to the same types of problems as the Q version?

Is there anyone on the forum with experience with these units?

Would anyone like to guess as to a cause of my problems or even better a potential solution?

Many thanks!

John
 
I have the Osram light@day fog/daytime running LED lights on my Fsi and have them same behavior when a mains charger is connected! But I do not have any problem with battery discharge.
I think you can rule out the DRL as the root cause to your problem.
 
Hi John,

I think there has been a few cases where things to do with the central locking have caused the battery to discharge. If I recall correctly, it's where there's a fault with one item on the CAN network, which keeps itself and everything else 'awake' so to speak, hence the battery drain. :p

As a start, I'd recommend putting a multimeter in series with the car's battery and measuring the current with the car locked. I can't remember the value of what it should be, but I'd then recommend checking if the current drops when items like the CCCU and door control modules are disconnected one at a time, with all of the fuses still in. If the current drops when say, the drivers door module is disconnected, then a fault may lie there.

Regards,

Matt. :)
 
I had a dealer look at the car and they did not find anything but suggested either a knackered battery or the DRL.
There are no faults indicated when scanning the car. Presumably something keeping the system awake should raise some flags?

John
 
John have you checked your battery condition
A healthy battery should be giving 12.4v at minimum from cold, any less than that and your battery will run down and possibly not even start the car after a week or so of sitting!
 
The battery is a two month old Varta from Audi.
The health window is as it should be. The car has in the past couple of years killed two batteries and so now I am determined to fix the cause.
 
The battery is a two month old Varta from Audi.
The health window is as it should be. The car has in the past couple of years killed two batteries and so now I am determined to fix the cause.

As Matt suggested, connect a multimeter in series to the battery (off the live terminal) when the car is locked, removing and replacing fuses in turn - this will definitely identify the culprit system. Whatever you do, don't try starting the car whilst the multimeter is part of the circuit!

I had a similar problem to you even after a new battery was fitted, and in-fact the drain was caused by an electrical mod whereby the rogue (but fused) system was still drawing current. Removing it took my dormant current draw from nearly 1 amp to less than half that. Good luck!
 
I have finally got around to digging into the battery issues. Until now I have been parking in a secure car park and so have just left the boot open and the negative terminal disconnected.

On plugging a multimeter in line with the battery on the negative terminal I can see that the current draw with a door open and the interior lights on is around 1A. This is probably a bit high.
With the doors closed and locked the figure drops to between 0.6A-0.4A. This is also way too high.

I have therefore tried to isolate the problem. I have found the following:
Fuses 36 and 41 appear to be responsible as when both removed the meter shows 0A occasionally hopping to 0.1A.

I have tried leaving 36 & 41 in and removing fuses 39 and 41 (left and right doors) this changes nothing and still shows >0.4A draw.
The drivers door seems to be operative with left door fuse removed and so it could be the door control module in this door.

So even though there is occasionally some noise coming from one of the door locking mechanisms (right hand side I think) but removing the fuse for this does not seem to help.

I think that the battery issues only began after I upgraded the interior lights to LED lamps but if they are not lit they should presumably not draw current.

Would it be worth removing all of these bulbs prior to looking more at the CCU? I am a bit baffled as to what is happening as there is not any obvious strange behaviour and the problem is stopped by removing fuses 36 and 41.

Are there any other fuses that could be worth a check to pinpoint more precisely? If a door module or similar was faulty would they stop drawing current when the CCU fuses were removed? If it is connected to CAN bus but no communications are occurring would the unit stop using power?

Is it possible to switch any A2 CCU for another just to see if the current draw drops. It would obviously not be coded but would it work enough to show that the current CCU is at fault?
If I recall the CCU has 4 or more connectors on it? Is it possible to remove these one by one to show which group of functions a fault is in? Is there an easy way to unable a door control unit?

This kind of problem keeps getting more complicated the more I delve.

Thanks!

John
 
I have finally got around to digging into the battery issues. Until now I have been parking in a secure car park and so have just left the boot open and the negative terminal disconnected.

On plugging a multimeter in line with the battery on the negative terminal I can see that the current draw with a door open and the interior lights on is around 1A. This is probably a bit high.
With the doors closed and locked the figure drops to between 0.6A-0.4A. This is also way too high.

I have therefore tried to isolate the problem. I have found the following:
Fuses 36 and 41 appear to be responsible as when both removed the meter shows 0A occasionally hopping to 0.1A.

I have tried leaving 36 & 41 in and removing fuses 39 and 41 (left and right doors) this changes nothing and still shows >0.4A draw.
The drivers door seems to be operative with left door fuse removed and so it could be the door control module in this door.

So even though there is occasionally some noise coming from one of the door locking mechanisms (right hand side I think) but removing the fuse for this does not seem to help.

I think that the battery issues only began after I upgraded the interior lights to LED lamps but if they are not lit they should presumably not draw current.

Would it be worth removing all of these bulbs prior to looking more at the CCU? I am a bit baffled as to what is happening as there is not any obvious strange behaviour and the problem is stopped by removing fuses 36 and 41.

Are there any other fuses that could be worth a check to pinpoint more precisely? If a door module or similar was faulty would they stop drawing current when the CCU fuses were removed? If it is connected to CAN bus but no communications are occurring would the unit stop using power?

Is it possible to switch any A2 CCU for another just to see if the current draw drops. It would obviously not be coded but would it work enough to show that the current CCU is at fault?
If I recall the CCU has 4 or more connectors on it? Is it possible to remove these one by one to show which group of functions a fault is in? Is there an easy way to unable a door control unit?

This kind of problem keeps getting more complicated the more I delve.

Thanks!

John

Hi John,

I think it's unlikely, but having said that it would seem sensible to try removing your LED bulbs and monitoring the fault again.

Re. changing your CCU without coding; I think this is probably feasible for the purpose of testing. The main issues that spring to mind that you may encounter are the remote central locking will not function off the FOB and if the donor module is coded differently for rear electric windows when compared to your car then you may encounter issues with the rear central locking. Other coding discrepancies will only result in relatively minor issues I think.

I am travelling at the moment so haven't got access to the A2 fuse arrangements/wiring diagrams. Do you know which features are powered by fuses 36&41? If they are items that send/receive information on the comfort CAN then I would suggest it is worth looking at disconnecting your drivers door control module and monitoring the quiescent current again. This is relatively straight forward, just requiring the removal of the door card. Based on the size of the drain you have and the fact that it is shared over more than one circuit suggests that a plausible explanation would be that it is being caused by a few items not entering a 'sleeping' state, possibly caused by a software/hardware malfunction by one of the items on the aforementioned CAN network.

Hope this helps.

Cheers
Rob


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Many thanks! The drain seemed to be worse when the car is damp and so something in the door seems likely.
I think I'll give this a try.

Is it only the control module on the drivers door that can will drain current when the CCU fuses are pulled?

Thanks for all the help guys! I finally feel I am starting to make progress.
 
It was the door lock. Once the lock was disconnected the power drain has gone!
Would the correct replacement part be 8Z1 837 016 E for a 1.2 TDI?

Great news! Do you mean the lock that's behind the exterior handle or the door control module that is just behind the door card? In my experience it is the door control module that causes the issue and the part number should be fairly easy to see on the physical part.

Glad the info helped.

Cheers
Rob


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Hi Rob,

I only disconnected the lead that is numbered 22 in the image.
This has disabled the door sensor and all the other problems.

A2 door.JPG
 
Interesting John. I wouldn't 100% rule out the issue not being caused by the control module though. It maybe that the module changes state when it has no signal at all from the door lock. I guess you will have to start by plugging in a good lock though. Audi/TPS should be able to tell you the correct part number from your VIN.
Cheers Rob.


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