battery drain in 4 days - how to trace?

russellbridge

A2OC Donor
Hi all

I've had the A2 ('02 1.4 Tdi SE) for 3.5 yrs now, and it's been used almost every day. If it's left for more than 4 days without use, the battery drains completely. This first happened a couple of years ago when we were away in Devon, and I couldn't remember whether I'd left the iphone charger in the cigarette lighter. When we got back I replaced the battery (it looked like the original one) with a new one as recommended by Mike (Varta Silver IIRC) to elliminate this as a potential issue.

Since then it's been left a few times for 4 or 5 days and on return the battery is completely drained (ie no central locking or anything...) It charges back up OK, and seem to be OK if it's used every few days. So as far as I can tell, the car has had the same problem since we got it.

The only mods are the underbody aero mods and aero wiper. No ICE mods - its on the original Concert II stereo.

Has anyone any ideas how to trace where the battery drain could be? The problem is that we very rarely leave it for more than 3 days to test...

Many thanks
Russ
 
Last edited:
I guess you could try removing fuses to various circuits to try and find which is losing power?
Also I guess scanning with VCDS to see if any circuits report being open/anything else odd?
The other option is to look at the fusebox and remove anything unnecessary and then add them back one by one and see what happens.
If the battery goes flat so quickly a volt meter measurement in the evening and one in the morning and removing fuses one by one my help identify where the loss is?
Admittedly this is just an idea based on problem tracking with computers and such so may not work...
 
I think that the best way is to fit a meter in-line with positive terminal of the battery.(I have a "Fluke" 75 multimeter) With everything off on your A2, and with your meter set to DC, amps, there should be no current flow. Now, if there is, then that is why your battery is discharging! Next, move along those fuses, removing one at a time. Look at the meter and see if there is any change i.e. down to zero. Using this method, you will find the guilty circuit! Be very careful to avoid touching the negative terminal on the battery, though!

David
 
...With everything off on your A2, and with your meter set to DC, amps, there should be no current flow.

Not true, I'm afraid. A few bits and pieces continue to draw current, such as the immobiliser, CCCU and door control modules. The CCCU contains the antenna that receives commands from the remote fob, etc. Some power is needed to keep this functional.
David's suggested method has some merit, but it's not quite as simple in practice.

Tom
 
Point taken, but there would appear to be a significant current drain. You would not get a battery "going-down" in just 4 days with normal operation? So removing one fuse at a time and then replacing it, and recording any change in meter reading, will give a picture of where the problem lies ..... Checking back might show that the removed fuse might have nothing to do with the immobiliser, CCCU and door control modules. It is useful information...

David
 
Thanks for the suggestions. David, if you've got a multimeter, is there any chance that you could do the positive in-line test on your car and let me know what the DC Amp reading is? As Tom notes, I'd assume there would be a trickle for immobiliser, CCCU etc. (just so I've got an approx figure for reference)
Would a standard analogue multimeter be capable of being connected in-line or would the current draw be too much? (assuming of course I don't try to start it!)
Russ
IMG_4318.JPG

edit: the Multimeter is only rated up to 250mA which I assume won't be enough - I'll have to borrow one off a mate.
 
Last edited:
Point taken, but there would appear to be a significant current drain. You would not get a battery "going-down" in just 4 days with normal operation? So removing one fuse at a time and then replacing it, and recording any change in meter reading, will give a picture of where the problem lies ..... Checking back might show that the removed fuse might have nothing to do with the immobiliser, CCCU and door control modules. It is useful information...

Sure. You'll note that I said your suggestion had merit. I was just correcting your statement about looking for a zero reading.

---

As an aside, I did this test within the first few weeks that I had my A2 and calculated that, based on the battery's total charge capacity, an A2 TDI should be able to stand for between 3 and 4 weeks based on the trickle current. Sadly, I can't remember precisely what the reading was, but it was small... 200mA-ish...?
 
Right
I've now bought a digital multimeter capable of reading 10A dc from maplin and some clamp leads so I can leave the multimeter in place whilst I play with other things
So if I hook it up and leave the car for 15 mins to go to sleep, it settles at around 0.47A
Taking all of the fuses and relays out drops it to 0.08A
Then the fuses which make a difference are:
Fuse #42 (interior lights, central locking) 0.27A
Fuse #36 (central locking, interior lights, air con) 0.37A
Fuse #2 (radio) 0.42A
Fuse #1 (instrument cluster) 0.50A (this may be a temporary surge)

All of the fuses are back in place now, doors closed, and its steady at 0.42A
If I take all interior bulbs out (1 in boot light, 2 in rear light, 3 in front light) it stays at 0.42A. With the central locking/ alarm activated, it drops to 0.37A

Missspentyouth's post here http://www.a2oc.net/forum/showthread.php?17516-Flat-Battery&highlight=flat+battery suggests that fuse 36 and 42 indicates a problem with the ccu and sending it off to lau may be in order

Are there any ways to test the interior lights further or should I just ship the ccu off?
 
Last edited:
Thanks for your tip bretti. I've taken the ccu unit out now and left the car for a bit, but the current draw is still 0.28A (I can't lock the doors and the interior light don't work). This seems too high?
FYI the CCU is 8Z0 959 443 Q.
Any thoughts on ways to test the interior lighting circuit?
Cheers
Russ
 
Just had another play but no luck, current draw still at 0.42, or still at 0.08 with all fuses out. For comparison, my father in laws a4 is at 0.03 as a resting figure, which is around the figure I'd be expecting on the a2.
A few of the vw sites mention a faulty diode on the alternator? Any other ideas to test?
Thanks
Russ
 
Hi russellbridge did you manage to sort the problem ? I have a similar problem but mines drawing around 4-5 amps ( with interior lights off) so as u can imagine within a few hours my battery is completely flat! I've tried taking the fuses out and the ccu but still draws around 4-5 amps I'm planning on disconnecting the alternator today to see if it is that drawing as can't think what else could draw that amount ?!
 
Hi Everyone,

I thought I had better update this thread as I ended up with Russ's car and getting to the bottom of the quiescent current drain, as a couple of you already know! As you can see if you look back in this thread, Russ had already done quite a bit troubleshooting - pulling fuses and measuring the resulting current drain with an ammeter. The drain was approximately 0.4 Amps but no one fuse/circuit seemed to contribute the whole of this amount which made it difficult to trace. The sleeping figure of a standard tdi A2 should be around 0.05 Amps - the central locking FOB receiver always stays active leading to a little current being drawn. What current measurements showed (I used a clamp meter around the main negative lead to the battery to measure) was that the following circuits did not appear to be going to sleep: Climate Control (0.08 A quiescent), Instrument cluster (0.12 A quiescent), radio (0.08 A quiescent) and CCU (0.05 quiescent on top of what should be expected due to the remote FOB receiver).

This really puzzled me, it seemed that there was something stopping all these modules going into a sleeping state. After a refresh of the A2 electrical architecture with a look at the wiring diagrams the one thing linking all of these items is the CAN BUS. I figured that for some reason, an item in the CAN wasn't letting everything go to sleep, either that or a possible wiring issue. I decided a wiring issue seemed unlikely as every other feature supplied by the CAN seemed to work faultlessly. I therefore decided, in turn to swap the mentioned units (CCU, CC unit, radio etc) and monitor the drain as each was changed. None of these seemed to eliminate the drain so I had another think. The only two units on the vehicle that were also linked to the CAN Bus that I hadn't swapped were the door control modules (2 only, as the vehicle does not have REW's).

I decided to take off the drivers door card and unplug the connector with the CAN wires to the door control module. Immediately, the drain shown on the clamp meter in the boot dissipated. Hey presto! I then tried plugging in a known good controller, locked the car, monitored the drain and yep, as you would expect there was only a drain of 0.05 Amps. It looks like either a software malfunction, or a fault on the circuit board of the control module led to it not sending out a 'go to sleep' signal to all of the other controllers on the CAN. What made it difficult to track down was the fact that clues were minimal - the control module/door micro switch etc worked faultlessly and there were no faults logged on the diagnostics. I've encountered many a faulty door control module, but never one like this before.

I hope this info is useful to someone and maybe if someone has a similar issue in the future they will be able to pin point the problem a little faster with this heads up :)

Cheers

Rob.
 
Top man Rob - thanks for updating the thread. I feel a bit better now about not being able to find the culprit - I'd never have got there in a thousand years! Hope the car's all well for you...
Russ
 
Thanks for this helpful thread - I have just tried to start my (late 2000) 1.4 petrol after 2.5 weeks only to find that the battery is completely dead. The battery was replaced only two months ago with a Duracell Type 096 (Advanced DA74) and I've had no problems staring after leaving the car for a week or so; the only use it typically gets is long motorway runs.

I would expect the battery to be fine for at least a month (or at least, to have *some* charge left), so will have to get a multimeter out and check the residual drain..
 
Back
Top