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Discussion Starter · #1 ·
So I've had my mk4 (v6 4mo) since March 2019, was supposed to be my daily, but it's kind of been something I need to sell since about 2020. Consequently its spent alot of time sat about not up to much, I drive it on occasion but now when I did want the drive it, the battery was dead. The battery was replaced in November 2019 as it was a battery that was at least 10 years old and I got a bosch one too!

It's gone flat a few times over the past year in just weeks, which I don't thinks right. When I got the car in 2019 the passenger door lock switch wasn't working (no interior light) so I replaced it with a cheap after market one thinking that might be a problem, now the drivers door lock is doing the same (although I have a new one in the garage).

But I wondered could the quick battery drain (from full charged to dead in 10 days) be an alarm issue where the car can't see the doors status properly?

It's on my list today to try and change it. But I wondered what else could cause such quick drain?

At this stage I don't really want to outlay any more in the car as I need to get rid of it (I have too many vehicles) but of it needs too much spending on it I need to just sell it as a project for someone and grumble about it.
 

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Yep its possible for a good battery to go flat in 10 days. I bought new in july/Aug of last year, went away on holidays for 14 days and when I came back she was deader than a dodo. I know what my problem is thou, I installed a live for my USB ports and then ran the neutral/ground to a grounding spot and not back to the battery like I should've done. It's a nice constant drain that I've still to resolve...

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So I've had my mk4 (v6 4mo) since March 2019, was supposed to be my daily, but it's kind of been something I need to sell since about 2020. Consequently its spent alot of time sat about not up to much, I drive it on occasion but now when I did want the drive it, the battery was dead. The battery was replaced in November 2019 as it was a battery that was at least 10 years old and I got a bosch one too!

It's gone flat a few times over the past year in just weeks, which I don't thinks right. When I got the car in 2019 the passenger door lock switch wasn't working (no interior light) so I replaced it with a cheap after market one thinking that might be a problem, now the drivers door lock is doing the same (although I have a new one in the garage).

But I wondered could the quick battery drain (from full charged to dead in 10 days) be an alarm issue where the car can't see the doors status properly?

It's on my list today to try and change it. But I wondered what else could cause such quick drain?

At this stage I don't really want to outlay any more in the car as I need to get rid of it (I have too many vehicles) but of it needs too much spending on it I need to just sell it as a project for someone and grumble about it.
I'm having the same issue - amongst a couple of other electrical gremlins. I also thought it might be down to the potato doorlocks.
 

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yes it could well be the duff doorlock that is draining it, and the worst bit about the battery drain is... no matter what brand of battery by the way, if it happens to often the batteries lifespan is seriously reduced. I had a battery drain on my old mk4 that would drain a 100 amp fully charged battery in a matter of 3 days... I never found what caused the drain but all the doorlocks including the boot were working as it should. so not alarm related on mine, i did pull fuses to find it but never got to the bottom of it as, i scrapped the car after it hit 470k miles and the biggest costs it needed were a new clutch and a complete respray... i just drove it to the scrappy instead.
 

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yes it could well be the duff doorlock that is draining it, and the worst bit about the battery drain is... no matter what brand of battery by the way, if it happens to often the batteries lifespan is seriously reduced. I had a battery drain on my old mk4 that would drain a 100 amp fully charged battery in a matter of 3 days... I never found what caused the drain but all the doorlocks including the boot were working as it should. so not alarm related on mine, i did pull fuses to find it but never got to the bottom of it as, i scrapped the car after it hit 470k miles and the biggest costs it needed were a new clutch and a complete respray... i just drove it to the scrappy instead.
I was planning on replacing the speakers anyway so if i'm doing a day with the door cards off I can replace the locks. Looks like it's a bit fiddly but not exactly difficult.

As for the battery it's probably already compromised cause it's happened a few times now.

470k is actually an incredible life span, mine's at 160k and 20 years old so it's at that awkward bit where loads needs replacing but in general it's actually still super solid - having said that I'm currently in the the "f*ck this I'm selling it" phase 😆
 

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yeah it did me well, and at that mileage it wasn't a real option to sell it on... so it went to the scrappy. In your case if the paint work is good i would just sort it and keep going :)
 

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Discussion Starter · #7 ·
So with regards to door locks and the alarm, I figured the mk4 has a disable ultrasonic detectors button like the mk6 I have, which is illuminated the reddy colour, if all the locks are working, does it turn yellow when you press and hold it for a few seconds like the later cases do?

I've replaced the other front door lock now, so both front door locks are new reproduction, boots original but seems fine, I tried the button but didn't know if it was supposed to change colour.

I've also replaced the fob batteries as they weren't working, the weird one was I had the engine running and the alarm went off, how is that even possible? It was before I changed the fob batteries though.
 

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Discussion Starter · #10 ·
Well 2 weeks and the battery went flat again, different battery which is older but always good from another vehicle, going to start driving it daily this week so hopefully that'll sort things out.

At this stage I can only think maybe the radio or I'd heard alternators can be a problem, I'd rather not need to spend anything more on it though!
 

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Well 2 weeks and the battery went flat again, different battery which is older but always good from another vehicle, going to start driving it daily this week so hopefully that'll sort things out.

At this stage I can only think maybe the radio or I'd heard alternators can be a problem, I'd rather not need to spend anything more on it though!
I hear you, same with mine I don't want to spend much more on it if I can help it although it's eventually going to need the turbo doing.

As for the electrics my eye is on the stereo, if not that then door locks, if not that then maybe I just sell the feckin thing 🤷🏻‍♂️

Annoying aren't they.
 

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You've got a problem charging the battery up if you don't use the car very often. Take it out and stick it on a mains charger then see how long it lasts before you jump it again. If you're leaving it on a driveway and not much else, battery will last 10-14 days then die. Doesn't matter how new it is. Don't keep doing this though or you will damage your alternator and possibly the battery. Drive it/let it idle for 10-15 mins once a week without the HVAC/radio on or put a trickle charger on it when not in use.

The interior motion alarm in the car isn't going to make much difference to how long the battery lasts. The button was mostly designed for those who leave pets in cars while the owner has gone into a shop/back inside the house quickly while the car is locked with them still inside. (You don't need to turn it off at the button on the b pillar, you just need to press the lock button on the fob twice. Then it's off until car is locked again.)

If the radio was the problem, you'd have found out very quickly, ages ago...
Faulty door locks don't tend to drain batteries.
Low car or key fob battery can cause a car alarm to go off at random even with the engine on.
 

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I disagree with the above, doesn't seem normal to me for it to die after 2 weeks of sitting.

Back when my battery was only 16 years old, I left the car sitting for over a month while I was away, and it started first time when I came back.

Something isn't going to sleep, or is randomly waking up and draining the battery. As northpole suggested, you can pull fuses for different circuits and see if you can narrow down the cause of the drain. You can either do this before letting the car sit, or if you have a multimeter then you can connect it in series between the negative strap of the battery and the negative terminal. After that, push the latches of the bonnet and driver's door into the shut position with a screwdriver, but leave them open. After a few mins, the car will go to sleep, then watch for an amp reading on your multimeter. Remove fuses one by one until the amp reading reduces to within spec, think it's below 0.1 amps to be within spec, but that's just off the top of my head so could be wrong.

If it were me, I'd start with pulling the fuse for the constant live to the radio before leaving the car sitting, and see if that resolves it. Fuse 42. If it's not that, I'd disconnect the loom going into the passenger door, while it's unlocked, then let it sit. That should confirm if either radio or your aftermarket door module.
 

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Discussion Starter · #14 ·
So it gets worse, Saturday the battery was fully charged, had it on charge in my garage for a while first(it was fully charged) put it on the car and the one that was on there was dead it started up and I had it running for about 15-20 mins, moved it round on the drive and left it overnight.

Yesterday I pressure washed it to get rid of some of the green then started it up and ran it for 10 mins. I did a check of the battery the day before and yesterday and it had dropped to around 12.3v which seems a little low considering it was like 13.8v Saturday when I put it on the car.

I came out this morning to go to work (was really cold overnight) and I struggled to unlock it, it wouldn't start as the battery was flat, in just 2 days!

At this stage I'm thinking more like what I have heard from alternators going, but why would it do that?

Looks like an arse of a job, so at this stage I'm thinking to just sell the car for 1k and let someone else fix it as its a fairly clean vr6.
 

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Discussion Starter · #15 ·
So I am still chasing down this fault as I've been a bit busy to get on with diagnosing, the other weekend I put the battery on which was fully charged and had stayed fully charged for a couple of weeks off the car, I disconnected the big black cable from the alternator at both ends, so only the light connection would be connected (which means it only connects if the ignition is turned on) getting rid of the way they can normally drain out.

The battery lost about 0.5v in 10 minutes, but I assumed that was the alarm coming back to life and charging up its internal battery, plus a few other things coming back on. So I pushed the bonnet catch down, double locked on the remote and then didnt have time to check the voltage until this weekend. Battery completely dead!

So I am wondering what things can drain the battery? It used to be ok. I am thinking there are 2 things that could drain the battery:
1) the radio, not sure how, but maybe if it was keeping the amp alive with do it in such a short time
2) the alarm, but what on earth could be causing it? I have changed both front door locks, as when I got the car, the passenger one didnt bring the interior light on, then the drivers side one failed, so I replaced, but other than that it seems to all work fine.

Running out of ideas at this stage.

Is there a way with something like VCDS to permanently deactivate the alarm so I could rule that out?
 

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Discussion Starter · #16 ·
OK so I have gotten to the problem I think finally and its a serious one!

While I was rigging up my multimeter in the engine bay I noticed how instantly the car was drawing several amps on multimeter, I locked the car and it dropped to a out 1.3amps which explains how the battery goes flat so quickly, I figured while I'm here I'll just pull the fuse to the amp so the meter dropped to this:
Grey Plant Red Gas Audio equipment


That seems like what I'd expect from a locked car with just the alarm doing something minor.

So I went in the boot to look at the amp, I have a factory foam load liner which when I lifted had a bit of water under, I thought out maybe damp has effected the amplifier, yes it had, bit more damp than I was expecting though....
Hood Automotive tire Motor vehicle Automotive exterior Bumper


Literally full to the carpet level!

Ive pulled everyth8ng out and pulled the bung out the bottom so it's drained out, the amp is a bit worse for wear though...
Rectangle Road surface Wood Asphalt Tints and shades


Now I need to work out how so much water got in the boot, I'm thinking tail light seals, but still not convinced!
 

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Potentially seal on the aerial. I think bumper vents are too low down, but don't rule them out completely.

Worth stripping out all the linings around the boot and laying down newspaper everywhere, then spray a hose over the rear end to see if any water traces appear on the paper. Should give you a rough idea on where its coming in from.
 

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That'll be your rear light clusters, rear washer motor and seal on the boot. Or maybe not all 3 but 1 at least. That's a lot of water though! When was the last time you opened the boot? I'm surprised you couldn't smell it...

The amp though is fubar'd. I'd also recommend checking the wiring going to/from it as water will track along it...
 

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Discussion Starter · #19 ·
That'll be your rear light clusters, rear washer motor and seal on the boot. Or maybe not all 3 but 1 at least. That's a lot of water though! When was the last time you opened the boot? I'm surprised you couldn't smell it...

The amp though is fubar'd. I'd also recommend checking the wiring going to/from it as water will track along it...
I dont use the car often to be honest, since the last MOT its only done a few hundred miles as its not my daily.

When I got the car it had been pressure washed and I did find a bit of moisture in the wheel well, but dried it and did some checks, turned out one of the tail lights was missing its seal, so I made one up (using neoprene draft seal because thats what I had, and it sealed better than OEM) but not sure when it started leaking. I dont go int he boot that often, but I get the feeling this has to have happened during this winter whatever it is.

While theres a bit of water damage at the end of it (coppers gone a bit black), for the most part its ok because the boot is the low part, so water cant track to far as far as I can tell. I'm going to see if I can get some more seals for the lights, the lights need to come off again anyway.
 
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