CAN BUS - Battery Drain - HELP!!

**iwadee** · 21-08-2020,03:39 PM

No change, garage spent a couple of hours and couldn't find anything, looked in the commonly offending places.
I've seen/read elsewhere about an isolation switch - anyone know or have experience with this?

**iwadee** · 22-08-2020,12:44 PM

Update - He couldn't find anything, checked in the normal offending spots, spent a couple of hours on it. We decided not to spend any more time on it as it will just keep costing more money.

Does anyone have any experience on isolating switches, that has also been mentioned to me? Fitting it inside the vehicle, saves opening the bonnet every time.

Thanks

**VAG-Abound** · 22-08-2020,01:03 PM

It's hard to fit them effectively in the cabin as its a very chunky cable, and ideally more chunky the further longer you make it. Also hard to fit safely as by definition it carries a high current to start engine so can't be fused to a level which is safe if there should happen to be a short circuit. Even in engine ones need careful fitting to avoid fire risk.

Do you really not want to get a multimeter and track it down yourself? I'll perhaps do some pics to help guide you.

**Crasher** · 22-08-2020,03:12 PM

I am surprised he could not track it down, using a multimeter with a 10amp current range it is very simple for someone with rudimentary knowledge of car electrics to establish the overall current drain and then begin the simple but tedious job of isolating the particar circuit. Fuse current testers (remember there are two main sizes) are very useful, the https://www.sealey.co.uk/product/563...ard-blade-fuse even shows them using it on the Golf 5 type PQ35 under bonnet fuse box.

**iwadee** · 23-08-2020,12:06 AM

I can buy a multi-meter and give it shot, and yes pics would be helpful.

@ Crasher - both mechanics said they'd narrowed it down to the CAN BUS area, that's all I know. I'm guessing that they did the MM test, pulling out the fuses, but I can only take their word for it!

Thanks for all of your help

**Crasher** · 23-08-2020,11:32 AM

If they pulled a fuse and recorded a drop they should have told you which fuse.

**iwadee** · 23-08-2020,11:38 AM

That makes sense. Will get one today and see how I get on. Need to watch a few guides on how to do it properly.

**VAG-Abound** · 23-08-2020,12:18 PM

Post a few more details like engine code, model / reg year and a picture of the in-engine fuse layout if you can. That'll help guide you on which slots to look at.

In-engine box will probably look like one of these, just say which if a photo is too hard to load:

**iwadee** · 23-08-2020,12:45 PM

Will do thanks. It's a 2005 plate, 2.0 TDI. I'll get the rest of the details when I get home, as it's sat on the drive disconnected.
If my battery is dead and I need to jump it again, a) do i go for a 20 min spin to charge it up again, or can I leave it running for the same amount of time?
b) how long after I switch the engine off do I start doing the MM test?

**VAG-Abound** · 23-08-2020,02:08 PM

If the battery has drained a couple of times it may already be in poor health, and a quick spin to get some chrage to then (probably) drain it again while finding tbe problem circuit will not help things. I'd again suggest getting a CTEC charger / conditioner to get it as good as it can be, tell you if it is past usable, and in the case where whatever the problem is doesn't make sense to repair straightt away can keep the battery happy between uses.

In the meantime, a good long single-start drive with no headlamps on way well get enough charge in battery to get started on tracking things down, depending on size of leak current.

I close car up and lool at current a half hour later. Others flick the bonnet and door latches so car think it is closed up and goes to sleep.