CAN BUS - Battery Drain - HELP!!

[iwadee]

Hi all

I've been having a battery drain problem on my car for months now and it has got progressively worse. I first noticed it in Feb, replaced the battery (it was on warranty), but if the car was left for a couple of days I'd need to jump it.
I only found this out when Covid started as I drove to work every day (20 min motorway journey). Working from home for a couple of days was when I spotted it.
I'm at a point now where I'm having to disconnect the battery after every journey. I'm also aware that constantly disconnecting it will no doubt cause more problems. If it's had it's motorway run, or driven for a while, even after 2-3 hours it'll go flat again. To the point where the electrics work, but not enough to start the car.

I've been to a couple of mechanics who frankly don't have the time to look at it properly. The error that has been coming up is the following : 00470 - Combination comfort Databus in Single Wire: Open Circuit
The first auto electrician I took it to said he spotted a drain and replaced the CAN BUS module, but within a day or two it was back to square one. The other garage spotted something similar and replaced another part (can't recall exactly what it was), but when I lock/unlock the car it makes a beeping sound, which never happened before. I know that you can change those settings when connected to VCDS/Carista etc.

I've also been told that it's a pain to find, as it takes a long time, testing different aspects/fuses etc. Obviously the time they spend on it adds to the bill and I don't want to keep throwing money at it.
Don't know if this is related, but my passenger and rear passenger window does not work from the driver console, but works from it's respective console. This happened in this time period, wasn't a problem before.

HELP!!!

[Crasher]

What is the cars year, is the radio the original and which part number CAN BUS did your chap fit?

[iwadee]

Hi Crasher

It's a 2005 (05 plate), original radio, and i don't know the part no. of the CAN BUS. However, I do recall installing a mp3/sd card player which connects to the back of the radio, but that was easily 2 years ago. Is the CAN BUS easy to get to, I could have a look after work/weekend?

[Crasher]

On the Golf 5 no, a right knuckle busting hand scratcher under the dash above the steering. We had a 2007 Jetta 5 in the other week, he had fitted additional parts to the OE head unit and the CAN BUS would not shut down so I fitted a new genuine unit and the problem stopped. CAN BUS units made before mid 2008 suffer this problem, you need the number off it which will come up with a code read.

[iwadee]

I have seen a couple of videos on where it is. Might give it a try later. What no. do you need off it exactly?
I don't have a reader either, borrowed it for a day.

[Crasher]

The VAG code prefixed with a three digit alphanumeric code such as 1K0, then 907 530 as the second and third group of numerals followed by one or two letters AND possibly a "colour" code such as Z00 so for example 1K0 907 530 or 7N0 907 530 BH Z00 which are actually the first to the current numbers with dozens of versions in between.

[iwadee]

After much wiggling and neck breaking, I think I've found it!

3C0 937 049 E - I've attached a pic, you can just about make the digits.

CAN BUS.jpg

[VAG-Abound]

I seem to have something steadily draining the battery. If I leave a multimeter plugged in place of the fuse for the convenience control circuit it takes a few hundred mA even after car is locked for an hour or so. Could be a door module, sunroof, etc so a bit fiddly to track down. Car is infrequently used, hence the slow drain means no start when it is needed.

My temporary solution is to put a CTEC battery charger / conditioner on it when not being driven. That's working very well in terms of me not having to think of a reason to go for a longish drive every few days to keep battery happy.

[VAG-Abound]

Getting an auto electrician to track down the drain can indeed be expensive and leave you without the car for a good while. If you're happy with basic electrics I can guide you through how I pinned down roughly where my drain was...

Using a cheap-ish multi meter (£10 at Screwfix) I firstly put it in the circuit between positive battery post and the cable that normally clamps there measuring high-current (10A) amps. If the draw is higher than the MM fuse limit it's going to pop it. Don't try to start car with this in place as it'll fry something. Closed up bonnet and car (otherwise something may stay awake), and checked it was indeed drawing a current an hour or so later.

I then got the engine bay fuse numbers for the circuits that feed other likely places, and tracked it down to one of those by putting MM in place of each fuse in turn. In my case the circuit feeding part of the under-dash ones was the culprit. Discovering which under-dash locations show 0V when the engine bay fuse is pulled tells you which ones to test for parasitic drain. So engine fuse back in and then pull each of the relevant under dash fuses in turn, seeing if drain at battery goes away.

This will disable some likely culprits like lock circuits, so you can't test them effectively. I got a pair of 4mm banana plugs, a couple of metres each of blue and brown of 2.5mm flexible wire stripped from an old appliance lead and a pair of mid-sized crimp on blade terminals to make up leads that could slot in place of under-dash fuse, so was then able to test the remaining few for drain while the circuit is still functioning.

[iwadee]

Thanks for that. It's gone in one last time to the garage, I've told him that I don't want to be throwing any more money at it.
Besides this issue, the car runs relatively fine. It does have 175 on the clock and I'm aware that I may not have that long left.
I've re-read your last post a few times, but electrics isn't my strength I'm afraid...!

Will let you guys know if he finds anything.