Hi all,

Chasing parasitic draw on my partner's 2011 Octavia 1.4TSI.

I've ruled out the alarm siren - removed it yesterday, and the battery had drizzled acid all over the PCB. Waiting to get a new one now. The draw still seems to exist, though maybe a bit better than before I took that out.

I decided to measure voltage drop across the fuses. Found a couple at 0.2-0.3mV; normal safe range. And one fuse at 2.2mV (about 150mA of current, approximately). It's fuse #39, 5A (I've double checked the fuse numbering, as that's confusing). According to the card by the fuses, I should read the manual about fuse 39. According to the manual it is not assigned! So I guessed it wasn't supposed to be there at all and pulled it; the clocks went off (time reset etc). Now according to the manual, the fuse for the clocks should be #6. I pulled that one and it also causes the clocks to lose power.

So how can I figure out what fuse 39 is up to?

Pic of the fuse box as it stands;

Let me know the VIN and I can find out what that fuse does.

Thanks!

TMBBJ21Z0B2091602

Is it possible you can give me a full list of the fuses, please?

There are two fuses for instrument cluster, an ignition switched supply from fuse 6, and a permanent supply from fuse 39 (on your car, not on earlier models).

Fuse 39 is also a permanent supply to the steering column control unit J527.

Thin red/yellow wires for both destinations.

Beyond my patience levels to define exactly all the fuses for any given individual car. Could probably be done, but would take hours with the resources I use (in this case a 4140 page pdf of all the possible electrics in an Octy 2 from May 2007 - April 2011; plus build date and a list of PR codes from your VIN).

What steps have you taken to assure yourself that the car is properly 'asleep' before these measurements are done?

Spot on, that's great, thanks.

Regarding the sleep...I haven't. Right now I'm just looking for anything that's drawing current with the car off/doing nothing. Fuse 39 is the only thing so far (other than alarm module, now removed). I think the next trick will be to rig up a remote fuse holder, so I can test it again with the car asleep, I think. And to investigate the instrument cluster and j527 superficially.

I know the (starter) battery is goosed right now, but even with the alarm module out it's still dropping from 12.7 - 12.5v overnight...and just manages to start the car from 12.4v. The voltage drop is steady through the night, so whatever's drawing current is doing it constantly.

Thanks a lot for the help so far!

How old is the battery?

If you have confirmed that the battery is 'goosed' you are possibly looking in the wrong direction by looking for parasitic draw.

How was the battery tested?

The overnight terminal voltage drop you are seeing is probably no more than you could expect - especially with a suspect battery.

Warrior makes a good point.

I spent a lot of time over the BH weekend assuming I had a parasitic drain on our Roomster, but found nothing, except a failed (very recent) battery.

To let the car shut down I found that just letting it sit, for around 15-20 minutes, after opening the door for access to cabin fusebox, was enough for the few fuses showing mV to go to zero.

The battery is about 3 years old. Varta. Parasitic draw has always been an issue, though it took me a while to recognise it. When she bought the car it had a connector attached to the battery terminals - clearly a quick connector for a charger, but I failed to join the dots. We replaced the original battery soon after buying because it seemed weak. And if the car was left for a week or so it would be weak too. In the past month or so it's got to the point that it needs to be kept on charge overnight, and like I say it'll struggle to start with anything under 12.4v.

So I'm 100% sure there is a parasitic draw - or at least was until I removed the alarm module.

Good to know regarding the sleep thing - wasn't sure if it would go to sleep with a door open.

Is there anywhere I can pick up a reference for the fuse layout on my car? I don't really trust it now, knowing the book is wrong.

6 hours ago, Tambohamilton said:

The battery is about 3 years old. Varta. Parasitic draw has always been an issue, though it took me a while to recognise it. When she bought the car it had a connector attached to the battery terminals - clearly a quick connector for a charger, but I failed to join the dots. We replaced the original battery soon after buying because it seemed weak. And if the car was left for a week or so it would be weak too. In the past month or so it's got to the point that it needs to be kept on charge overnight, and like I say it'll struggle to start with anything under 12.4v.

So I'm 100% sure there is a parasitic draw - or at least was until I removed the alarm module.

Good to know regarding the sleep thing - wasn't sure if it would go to sleep with a door open.

Is there anywhere I can pick up a reference for the fuse layout on my car? I don't really trust it now, knowing the book is wrong.

6 hours ago, Tambohamilton said:

The battery is about 3 years old. Varta. Parasitic draw has always been an issue, though it took me a while to recognise it. When she bought the car it had a connector attached to the battery terminals - clearly a quick connector for a charger, but I failed to join the dots. We replaced the original battery soon after buying because it seemed weak. And if the car was left for a week or so it would be weak too. In the past month or so it's got to the point that it needs to be kept on charge overnight, and like I say it'll struggle to start with anything under 12.4v.

So I'm 100% sure there is a parasitic draw - or at least was until I removed the alarm module.

Good to know regarding the sleep thing - wasn't sure if it would go to sleep with a door open.

Is there anywhere I can pick up a reference for the fuse layout on my car? I don't really trust it now, knowing the book is wrong.

6 hours ago, Tambohamilton said:

The battery is about 3 years old. Varta. Parasitic draw has always been an issue, though it took me a while to recognise it. When she bought the car it had a connector attached to the battery terminals - clearly a quick connector for a charger, but I failed to join the dots. We replaced the original battery soon after buying because it seemed weak. And if the car was left for a week or so it would be weak too. In the past month or so it's got to the point that it needs to be kept on charge overnight, and like I say it'll struggle to start with anything under 12.4v.

So I'm 100% sure there is a parasitic draw - or at least was until I removed the alarm module.

Good to know regarding the sleep thing - wasn't sure if it would go to sleep with a door open.

Is there anywhere I can pick up a reference for the fuse layout on my car? I don't really trust it now, knowing the book is wrong.

Important, the control modules will not go into sleep mode with a door open.

You have repeated that the vehicle struggles to start when the battery voltage drops to 12.4 volts - the battery is still 75% charged at that voltage!

Unless either the starter, the wiring connections to it - or the battery has a fault, there is no reason the engine shouldn't crank at normal speed - even down to around 12.0 volts (50%)

It is critical to know what the voltage falls to when the starter is operated, I suspect that the voltage is dropping critically low due to a battery fault.

Edited 11 May, 20251 yr by Warrior193
added information

Everything on our Roomster went to sleep with door open and no attempt to lock car.

Surprised me a little.

Reading the battery voltage of the battery when not loaded is not an indication of battery capacity. As batteries age, not only is the capacity reduced but they also look like there is a resistor in series with the output, limiting maximum cranking amps.

As said before, check the battery voltage when cranking or get a battery supplier to use their test equipment (usually free) to see how it performs under load.

A battery in good condition will be 75% charged at 12.4 VDC - agree, the only reliable way to test a battery is by imposing a known load and measuring the voltage drop.

OP appears to be chasing a possibly phantom parasitic load, while admitting the battery is 'goosed'

12 hours ago, Tambohamilton said:

Is there anywhere I can pick up a reference for the fuse layout on my car? I don't really trust it now, knowing the book is wrong.

The fuse diagram is a mirror image of the fuse box. Skoda use the same fuse card diagram for both LHD and RHD vehicles even though the fusebox is on the opposite side of the car.

6 hours ago, Warrior193 said:

A battery in good condition will be 75% charged at 12.4 VDC - agree, the only reliable way to test a battery is by imposing a known load and measuring the voltage drop.

OP appears to be chasing a possibly phantom parasitic load, while admitting the battery is 'goosed'

Yes, because I really don't want to put a new battery on it, only for it to get destroyed like this one has been.

1 hour ago, tetley said:

The fuse diagram is a mirror image of the fuse box. Skoda use the same fuse card diagram for both LHD and RHD vehicles even though the fusebox is on the opposite side of the car.

Issue isn't reading the card or manual - they're wrong/incomplete, so I'd just like to have the correct information for this car.

I know the battery is done for - replacement will be arriving in the next few days. The only question I need to work out right now is whether parasitic draw remains with the (very dead) alarm module removed, or whether the overnight voltage drops are just because the battery is toast. Simple solution but I just haven't had time: disconnect the battery from the car and see if the voltage still drops the same. And/or directly measure the current draw at the battery with the car asleep.

Thanks for the replies, I'll keep the thread updated with any developments...

The overnight voltage drop you are currently seeing will be normal - especially given the current battery is faulty.

Fit the new battery, carry out correct adaptation (coding) if required - E.G if vehicle has 'smart' alternator, then test again to check if there is any parasitic drain - which I think will be unlikely.

Provided the new battery is not discharged below 30% - below approx. 11.8 V for AGM/EFB (or 11.6 V for standard L.A battery) and the battery is recharged immediately after discharge, the battery will suffer no damage.

No coding required - dumb dumb alternator. Will certainly keep an eye on it when the new one goes in.

On 10/05/2025 at 14:33, Tambohamilton said:

Hi all,

Chasing parasitic draw on my partner's 2011 Octavia 1.4TSI.

I've ruled out the alarm siren - removed it yesterday, and the battery had drizzled acid all over the PCB. Waiting to get a new one now. The draw still seems to exist, though maybe a bit better than before I took that out.

I decided to measure voltage drop across the fuses. Found a couple at 0.2-0.3mV; normal safe range. And one fuse at 2.2mV (about 150mA of current, approximately). It's fuse #39, 5A (I've double checked the fuse numbering, as that's confusing). According to the card by the fuses, I should read the manual about fuse 39. According to the manual it is not assigned! So I guessed it wasn't supposed to be there at all and pulled it; the clocks went off (time reset etc). Now according to the manual, the fuse for the clocks should be #6. I pulled that one and it also causes the clocks to lose power.

So how can I figure out what fuse 39 is up to?

21 hours ago, Stonekeeper said:

Great, thanks for this. Nice to see fuse 39 actually listed! Where did you get it, if you don't mind me asking?

Am I right in guessing that it's just a generic diagram for the later model MK2s? Where would I find info that is specific to my car?

Edited 13 May, 20251 yr by Tambohamilton

On the skoda website you can find handbooks by vin number.

https://www.skoda.co.uk/apps/manuals/Models

I had to use trial and error around builds from 2010 to 2011 to find it because registration year can be the year after build.

I cannot remember which one had that particular schematic now.

Thanks. As is typical, it doesn't recognise my vin. But is an 11 reg car and the late 2010 manual doesn't stack up, so it must be the "2011/5" manual. I wonder if the car is just really close to the crossover date (hence new fuse layout but old manual), or one of the POs replaced the manual for whatever reason... Anyhow, at least now I have a better reference for fuses! Beginning with the 2011/5 manual, they no longer list fuse ratings. Can't have it all, I suppose!

New battery due to arrive today sometime...

Edited 13 May, 20251 yr by Tambohamilton

Build date was 23/12/2010. In car printed manuals are often insufficiently up-to-date, same with stickers of fuse info.

Sometimes copy/paste on something like a VIN doesn't work because of unnoticed leading or trailing space characters. Try typing it into the site that @Stonekeeper kindly recommended, character by character. And make sure all the 0 characters are entered as numeral zero, not letter 'oh'.

New battery is in. It's dropping about 0.1v overnight (12.9-12.8). I assume that's OK because it's over 12.7; it's not really losing significant charge (and way over any danger voltage)? Still, more of a downward trend than I'd hoped.

On 13/05/2025 at 13:53, Breezy_Pete said:

Build date was 23/12/2010. In car printed manuals are often insufficiently up-to-date, same with stickers of fuse info.

Sometimes copy/paste on something like a VIN doesn't work because of unnoticed leading or trailing space characters. Try typing it into the site that @Stonekeeper kindly recommended, character by character. And make sure all the 0 characters are entered as numeral zero, not letter 'oh'.

Finally got around to doing this on PC instead of mobile - worked straight away with copy/paste. Unsurprisingly the manual/fuse diagram is identical to what is in the car, so that doesn't help, but never mind!

New battery seems to be holding fine, so I'm pretty much assuming that the dead alarm module battery killed the last 2 starter batteries. I'll continue to keep a vague eye on it for a while yet though.

Where would be best/cheapest for me to buy a genuine alarm module? I'm not keen on messing with a pattern part, and the hassle they bring.

Edit. Ignore previous version here.

Wrong VIN pasted.

Edited 20 May, 20251 yr by Breezy_Pete