Hi,

I am trying to disconnect the 12 volt so I can install an amplifier (Match M 5.4DSP), but it's impossible for me to find any information on exactly how to do this. The service manual says the following:

(https://www.manualslib.com/manual/2070938/Skoda-Octavia-Iv.html?page=169#manual)

I've managed to find Europ NCAP rescue sheets that contain instructions for other VAG PHEVs like the Passat GTE, and they have the 12 volt in a compartment in the trunk. But that seems to not apply the Skoda PHEVs... The only relevant things I've found is a black bolted-on plastic cover in the trunk near the high voltage battery and a foam block covering what looks like a wire bolted to the frame (which must be a ground connection?).

I was thinking it might be enough to pull the infotainment fuse but I am far from confident enough to attempt any of that without some validation. For reference, this is the installation video I've been watching: https://www.youtube.com/watch?v=p_NEzQZraUY.

So my question is: Should I just admit defeat and get someone to do it? Or would any of you have something to share that could help me along?

Thanks!

8 hours ago, sqdk said:

've found is a black bolted-on plastic cover in the trunk near the high voltage battery

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...

Interesting, what is item 2 (stored gas inflator) used for - is for the airbags rather than using integrated pyro devices ?

@SkOmk4 I cannot believe I couldn't find that. My google-fu failed me... But thanks a bunch for the clarification. I have also found it myself now.

So, would you say that the procedure is then the same as with all the other VAG PHEVs? And would it be alright to do as a layman?

I am guessing I should start with disconnecting the HV system via the green switch in the engine bay, then disconnect the 12V, install my amp, reconnect the 12V and then finally the HV system. Is there a chance that the car needs to be coded after? I have seen this as part of some 12V battery replacements, but haven't been able to figure out if that is also necessary when just disconnecting and reconnecting it.

Again thanks for clarifying. Very helpful to get some assurance.

Have a look at the attached Workshop Manual pages (I had to cut the original file, since it has ~70MB size and the limit here is 10MB).

Seeing the procedure in the Manual, it seems to me there's no need to disconnect the HV system, but I'm no specialist. I'm guessing that when the 12V is disconnected, all the HV and high-power relays are off - so there's no actual risk.

AFAIK, there's no need to code anything after - since the battery is the same. When it is replaced - that's a different story. The Manual is warning that errors are normal after 12V disconnect/reconnect, but most users mentioned those errors are gone after a couple of complete steering-wheel turns left-right and after several driven kilometers (or miles if you prefer 😁 ).

34_Electrical_system - Car Service Repair Manuals and Wiring Diagram_reduced.pdf

Edited 4 September, 20254 Sep by SkOmk4

@SkOmk4 You're a legend, that managed to give me the confidence to proceed! Thanks a bunch. I'll contribute back with a Match DSP setup once i get it all dialed it. Just got a microphone today.

A little thing i could also contribute back is that there is a small lid in the compartment for the charging cable that shows a cable connected directly to the frame. That is actually the negative lead from the battery. So i didn't even have to take out all of the styrofoam and undo 8 bolts, I could just have made do with that single one... It was so conveniently placed that I suspected it might be for exactly this reason, but I didn't dare touch it until I was certain. Ended up just undoing that it it worked as expected...

Again thanks a bunch, couldn't have done this without your help!