Battery Draining Issue - Advice Needed

May 15, 2024
1
0
Hi All,

Over the last 6 months the battery of my 2018 Leon 1.8tsi FR DSG has been draining significantly faster than it should be. Leaving the car for more than a few days will fully drain the battery. In the last 6 months I have been to the main dealer twice, firstly to re-code the previous battery which I was told would fix the issue but didn’t, and secondly to replace and recode the battery again both at the same time. This solved the issue for a short period of time but the issue is now back and if I leave the car for a few days the battery will go flat.

Is this an issue others have had before? I would like to go back to the main dealer and explain the issue is still not resolved, but I am tired of paying a lot of money for the issue not to be fixed. I am wondering if it is worth going to an independent Seat specialist as they may conduct a more thorough investigation rather than the standard main dealer procedures which don’t seem to show any issues.

Any advice would be greatly appreciated, thank you.
 

mty12345

Active Member
Jun 17, 2011
3,777
478
bristol
Becoming a more and more common issue as cars have more and more modules in them. Sounds like one module is staying awake rather than sleeping as it should, but trying to find out which one it is can take a lot of diagnostic time. An experienced auto electrician is probably a better shout than most dealers.
 

cupra14

Active Member
Aug 31, 2017
342
65
England
I expect there's a time after which the car should have gone to sleep - anyone know what that time is?

The idea would be to wait till then and then see which part(s) of the car is/are still drawing more current than they should (should being near zero).

You can put an ammeter (meter on amps, well, mA) in series with a subsystem but it's a pain (because every time you want to try a new subsystem you've to mess around with connections AND you'll wake the car) so instead you can measure the slight voltage drop across each fuse. If no current the drop is zero (ohms law - a fuse is a resistor). Most fuses have tiny metal bits you can put a meter's probes on (have a look). Meter on mV as it's a tiny drop.

There are videos about this online.

You likely wan to defeat such as bonnet or door locks so the car thinks they're closed.

Note: needs patience, care, and a logical approach. Takes time.

You can practice on any easy to reach fuse and don't bother to wait - make sure it's a subsystem drawing power and that you CAN see a mV drop.

You're looking for what's sometimes called a quiescent current that's too high. Or, a parasitic current (i.e. the one that's too high).
 

RUM4MO

Active Member
Jun 4, 2008
7,851
1,007
South Scotland
20 minutes will definitely be long enough for the controller to go to sleep.

I think that any "noise" in the comms lines will keep wakening up some controllers.

Anyway, as the battery gets older, sometimes these problems "appear" ie maybe they existed in the background but your "car usage" pattern and the battery capacity has changed - and now there is a real issue. Edit:- probably not your battery as it has been changed I've just remembered.

I had that with my older daughter's 2009 SEAT Ibiza 1.4 SC, and there was a "known at the time" probable issue with the BCM programming of that spec of Ibiza at that production period, same for low spec VW Polo 1.4 of that production period, cars that appeared with a battery draining problem seemed to get sorted out quickly maybe as late as 2011 - it was a lot later than that before this issue showed up on that Ibiza while I was looking after it, so my claims of "there is a known issue" were ignored by the first SEAT main dealer, a year or so later I took it to another SEAT main dealer who just happened to have seen this issue with a traded in VW Polo from 2009, eventually sorted it out by updating its BCM software, so listened to me, took the car in, ran a full diagnostic check, found no issues, then requested help from SEAT Mothership as to where to locate the software update - car sorted! That was just an example of what can cause this issue - it cost me quite a bit as the first workshop found the steering angle sensor to be faulty and replaced that etc and charged me maybe £200 - and the problem returned - then that dealership closed - land was sold for housing!

So, for a quick check, with the ignition off, wait 20 minutes with the bonnet open, using a DMM set probably on 10 amp DC,with a crock clip on the main battery earth lead bare crimped connector tag at the end nearest the body, and a long sharp probe ended lead on the battery +VE post, slacken off the +VE battery clamp and ease the lead up "through" the long thin probe and off the battery post, observe the current reading. If you let either lead slip off, the 20 minute wait time needs to be repeated. Edited!

If you carried out the above test and the drain current was more than say 50milli amps - typically with a fault it will be a lot more than that, you might want to repeat that test so that you have a grasp of what the typical drain current is immediately after ignition off, ie when the controller are still awake - knowing that might be handy for later on.

Lots of these problems are due to crushed/sheared wiring and faulty, but still working alternators - and even wiring that has got pierced by fixings that the cable passes over. Edited!

Good Luck!

Edit:- at least on that 2009 Ibiza, I found that not bothering to trip the bonnet latch etc worked okay for me, I spent hours proving to myself that there was no electrical issues with that car - so I was proper p'd off when I needed to pay "experts" to say that they found the issue, at the second visit - first day in they declared NFF - I said, okay, keep looking, they diagnosed a failed "clock spring - winder tape assembly" replaced that, test car for another day, said job done, car still the same!! No harm in tripped the bonnet lock to fool the car into thinking that the bonnet has been closed though.

Another Edit:- it would be very helpful if you had access to a proper VW Group scan tool like VCDS just in case you cause any faults to get logged, like the airbag system etc.

I've just edited this posted at 3 areas to improve it!
 
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