SkOmk4

The black bolted-on plastic cover that you mention is hiding the 12V battery that you want to disconnect. Simply unbolt the plastic cover, and you'll have the access to the 12V battery connectors. FYI: what you consider to be "the high voltage battery" is in fact the fuel tank. The HV battery is under the floor under the rear seats - see screenshot of the Octavia PHEV Rescue Sheet and the legend therein...

If it opened normally, does the car still close/lock from remote? That would be a sign that 12V is still alive. With the steering on the proper side of the car ( I see you're in Finland) I suppose you can open the engine bay. Try to connect an external 12V there; there's a "+" connection point in the fuse box (no need to go directly to the 12V battery.

How did you turn off the speed warning? Is it managed by a module that is not SFD2-locked? I have the "good-old" SFD (not SFD2) on my Formentor, but I was just curios... I assume that by "speed warning" you're referring to chime that occurs when you go above the speed limit detected/seen by the car via TSR.

Ok, that's not great. You'll need to take pictures or a video of the error message if/when it happens again. It's really surprising that yesterday evening someone was reporting an identical situation on a Formentor facelift (same platform - 1.5 eTSI DSG): car about 5.000 km and it happened twice; once while driving and once stationary. As in your case, the dealership said they have no errors stored and can't diagnose the issue. (also not easy to reproduce - as it happens randomly...) This story looks to me very similar to the problem VAG had when they launched the facelift (Octavia, Formentor, Golf, even the new Tiguan). Every once in a while, the car was refusing to start (get in, press Start - no reaction). It was happening randomly, not on all cars, and mostly in wet weather - the dealership told me it was happening on some of the new cars after they were washing them for delivery preparations!!! The dealership would scan the car immediately and there were no errors to be found. Meanwhile, after plenty (I assume) of reports for that error/fault, I read that VAG released a SW update to address that issue. If I'm not mistaking it was a Gateway related problem. I'm guessing it will be a similar situation with the problem you reported, they need feedback from the users to identify and solve the root-cause of the issue. Just remember to record the fault...

Yes, that might also help, even though I'm not sure how well that works... So far I've read about several different situations: car throwing an on-board (major) error/fault (e.g. drivetrain), requesting immediate visit to the workshop - but no notification received by the "favorite service" - those seem to be most of the cases; car having no problem while driving and no fault in the "car status" on the infotainment, but owner receiving a call from the service saying the car reported some error, "visit us so we can check the car" - very few cases. Mine initiated 2 or 3 times a "breakdown call" - but that was clearly the faulty roof control panel with it's well-known problems. However, my "favorite service" never called me... 🥲

Indeed, there are plenty of glitches on the control-electronics side with this VAG generation (also affecting the platform "step-brothers" Golf, Leon/Formentor etc.). I am assuming that when the error occurred, the ICE was at zero rpm, and the driving situation needed it to be restarted - was it? And 48V failure implied that the starter/generator could not be used/energized at that moment... It is highly unlikely that it happens the other way around: the ICE is running and the 48V-failure stops the ICE. However, a failure of the 48V system - makes the ICE starting impossible. The big question is: did this failure leave any error messages stored on the car? That's what the dealership will look for when you report the problem. In some cases reported online, similar issues (such as failure to start the car and recovery after several minutes of waiting) - did not leave any stored-errors, which makes it difficult (if not impossible) - for the dealership to diagnose/fix the problem.

Is it a PHEV, or a mild-hybrid? The 48V message would indicate a mHEV... AFAIK the Facelift Octavia no longer offers a PHEV drivetrain.

Keep searching, there's definitely a usb-C & usb-A version - since I have it in my car - also a Sandisk IIRC. Unfortunately I don't have a link for you, since I have it from a local online seller, more than 2 years ago. L.E.: I was wrong, it's actually a Kingston. I love the shape - very compact for a double connector; here it is: https://www.kingston.com/en/usb-flash-drives/datatraveler-microduo-3c-g3

To add to the confusion of some users, have a look at the message I get on my VC when I disengage the Auto-Hold in my car... talk about idiots in charge of SW-development at VAG... 🤔

You need to pay more attention to that space between the front seats! The post-facelift model also has a "P" - next to the gearbox selector, for gearbox-park (pin-locking the transmission) and also a second "P" - next to the "Auto Hold" button, for the Electronic Parking Brake (EPB). So DO NOT press the blue-marked button in the attached picture, but DO press the red-marked one... note: having the Auto-Hold engaged when you stop the car, will automatically apply the EPB also; therefore, if you want to have the EPB-OFF, disengage the Auto-Hold before stopping the car...

Mine had a functioning LED in that position - produced Sept.'22, MY23

AFAIK that was the case for the 2.0 TSI engines, in the early years of the pre-facelft mk4 Octavia. As for the facelift model with the "revised" version of the 1.5 TSI model, all pictures/videos I saw were showing there's no more engine cover. It's just a small plastic around the oil plug - as in the picture below. Can you post a picture of your engine bay?

Yep, I mentioned that in the enumeration a few posts above...

Yep, with ignition on, I don't know how the 12V systems take/drane power from the HV battery - if it goes through the 12V battery or not. My previous statement was related to the "car parked and turned off" (e.g. overnight) - when most of the reported 12V battery drain occurred.

No, not only for the systems in the cabin; there are plenty of relays and low-voltage components powered by the 12V battery. Unfortunately there's no scenario which allows the HV battery to directly charge the 12 V battery. AFAIK the 12 V battery on our cars can be charged while: - driving in EV-mode; - driving on ICE; - charging the HV battery. I remember seeing such a diagram on some technical documentation posted on this Forum if I remember correctly.

I noticed that the switching to P (the gearbox park, not the EPB) might be noisier sometimes - single clunk as you say - depending on how you proceed: - if you press directly the STOP button while gearbox is in D/S or R, the noise will be louder; - if you press P (gearbox Park) before pressing STOP - the entire process will be quieter. Depending on the "flatness" of the surface you parked the car onto, if there's some slope, it might be better to first engage the EPB, press P after that, and press STOP at the end.

The ICE is started by the electric motor (that can be used as a motor, generator or starter), so it uses the HV battery.

It's actually a problem for ALL the VAG models (facelift or not) sharing the same platform and electronics - quite a long list. The issue is that this problem has some sort of probabilistic occurrence - some might encounter it a few times in a couple of days, others once or twice over several months. On top of that, only a few percent of the users are using the forums, so it's no big surprise you've seen too few reports. By now this problem is quite well-known by VAG and afaik there's a SW update to address this issue as I wrote a few posts earlier. A dealership saying they know nothing about this, is either playing stupid, or is just incompetent... Oh, wait - there's a third possibility: they only see 2-3 new cars over the entire year, so they never encountered that specific problem.

That's really weird... All car compressors I've seen (and there's been quite a few) had a long-enough cord to reach all wheels from a single 12V socket. For your Octavia: did you try to use a shorter path for the cord? You can fold one of the rear seats, and go from the 12V in the trunk, inside the car over the rear seats, and out the front door - to the corresponding front wheel. I imagine that is the shortest path.

Glad you found the solution and that it worked! I accidentally found it on mine after almost 1 year of ownerhsip - during my 2nd cold season with the car. Until recently I was also using the App - just as you mentioned. However, I fail to understand the logic of those programming the climate control. Why not start the heating from the "normal" Clima interface while waiting in the car? Why is it only possible via the "goodbye screen" of from the App? Is it a bug, or is it some sort of protection feature?

The heater is the same (as long as the heat doesn't come from the ICE) - it's a PTC heating element using energy from the HV battery. However, what you noticed and described in your post I think is some sort of software error (or just lazy programming) of the climate control unit - it has exactly the same behavior in my Formentor, which is basically the same car in different clothes. However, I found there's a solution for this lack of heating while using the in car controls with the car stopped (no engine, not "Ready") - probably there's some info in the User Manual, but who reads it 😁 ? . If you're trying to heat up the cabin via the infotainment controls - the same way you do while the car is running - it will only use the ventilation, but no PTC heating. So you'll have air at outside temperature blown inside your car. The workaround is to press the STOP button - as you do when you leave the car, and the infotainment screen layout will change to the "Goodbye" one. On the top/upper bar of the screen, in the left corner (that's on Formentor - might be different to Octavia) you have a "heating button" (see attached picture) - press that one and you'll have stationary heating, without using the phone App.

I've got some news from the Formentor group: one of the guys that experienced this problem during his vacation went to see his dealership yesterday. Surprise: they also told him it's a known problem, but apparently did more than that and installed some software update that's supposed to address this issue. Unfortunately, the guy who posted this piece of info was not curios enough to ask what module was updated, or get more details on the SW update - some version or TPI number (if applicable). On the other hand, my experience so far with the VAG group showed that Seat/Cupra branch is the last to get SW updates; of course, my statement is based on the delay they launch the infotainment updates. They were the last to release 1940/41, 1969 after VW and Skoda, and now there's no news concerning the 1985 version - while some Octavias receive it OTA. The point I'm trying to make is that if the Cupra guys installed an update to solve this known problem, I'm almost convinced the update is already available for the affected VW and Skoda models.

Sure, it's a strange statistical behavior... it might start without issues in pouring rain or out of the car wash, but fail to start in damp air (or vice-versa). As I mentioned, it's really difficult to reproduce the behavior - at least according to those encountering the problem.

🤣 If "my guy" at the dealership was honest, and indeed there are no errors stored after those start failures, then don't hold your breath waiting for them to solve the problem. More than that, with no errors and with a problem so difficult to reproduce, they'll have a hard time understanding (or even believing) there's an issue with the car. I suggest you make a video of the behavior if/when it happens again. Was the weather (and the car) dry or wet? I'm simply curios if it also happens in dry conditions; so far I've only heard of it occurring in wet, and only for the facelift versions of those cars I mentioned above.

I'm assuming it's the facelift version - therefore I have an idea about your problem, but no solution... As most of you know, Octavia 4 has a few other siblings - the Golf 8, the Formentor and the latest Leon; as such, they share lots of stuff... mechanically, electronics and as a consequence - problems! A few months ago I was discussing with my Cupra dealership as they were just receiving the first transport of facelift Formentors. He was telling me that when they washed the cars after the trip from Spain to Bucharest, about half of the 10 cars they received didn't start... They immediately scanned for errors - nothing stored!!! However, after closing the cars and waiting for a couple of minutes they start without any issue... 😇 On the other hand, over the past several months, on the Formentor online group we use here in RO to share useful information/solutions/tips, quite a few of those with the facelift model mentioned that their cars didn't start on few occasions, either after washing the car, or after rain overnight, even after heavy-fog... high-humidity being the common denominator. In ALL cases the car started without problem after some waiting time with the car locked. Since the problem you described in your first post reminded me of all the situations that I mentioned above, am I wrong to assume that on those mornings when you encountered the problem the outside humidity was high? Apparently there's no formal solution from VAG, no TPI... but it's already quite well known unfortunately. I even found online the same problem (and "solution") mentioned for the new Tiguan; they were mentioning some communication issues caused by the Gateway, but until there's an official answer from VAG - it's all just assumptions.