Thanks for answering. Fuel shouldn't be any problem I think because otherwise it should also not work properly in charge mode. As I mentioned earlier the spark plugs are just a week old. It was a little trip to the workshop where I changed the plugs. Before changing the plugs the car acted accordingly as I mentioned earlier. Right after we changed the plugs the car functioned properly, with zero electric range. A couple of hours later on another trip te car had the same issues again. I also don't think that the 12v battery is an issue because that should also generate problems with the initial start of the engine. Save modus I did not try yet.
No the 12volt battery is not involved with engine starting, There is no starter motor, the Motor/Generator is driven as a motor from the Drive Battery to start the ICE. If the Drive Battery is dead then it won't start, It should never get to that point as there is supposed to be about 25% held in reserve for Hybrid operation when the EV range reaches zero. I find that when my engine starts I feel it slightly lose power. so the current from the battery being diverted to starting the engine is causing a loss of drive. If your Drive Battery is really run down that jolt you mentioned and non starting is likely.
I'd be more focused on the battery capacity and what the actual full charge range is, maybe a DBCAM and reset of the BMU could be useful. My 2018 (NZ) model had a DBCAM recently and range improved by about 20% so the guessometer really is just guessing about some stuff, maybe the reserve capacity is one of those things. PHEV watchdog might give you some indication of what the capacity is when the problem occurs.
There is one thing that really surprised me a couple of times, I have an OBDII Bluetooth adapter so I can use the PHEV Watchdog on my phone. I used to leave it plugged in all the time. However, a few times I have had several warnings come on like EV system servicing required and similar warnings about braking etc. These have occurred while driving but only while the OBDII adapter was plugged in. Stopping and restarting seemed to solve that, but I don't leave the adapter plugged in anymore. Similar warnings have been seen when the 12 volt battery was running down due to sitting around powered on with the radio on maybe with auto headlights on as well sitting in the shade, not too sure, may have been in accessory mode which should shut off after 30 minutes so maybe the battery was suspect.
I had a very weird issue with the 12volt battery. I went to plug in one night about 4 hours after getting home on a normal day, but the car was dead. Nothing worked and it stayed locked. I used the key to open it and opened the bonnet, checked battery voltage on the charging lug in the fuse box, about 2 volts. No idea why this happend or even how it could. Unless powered off it can't be locked, if inside light is on it will shut down sometime, that was not on anyway. I could not charge because both smart chargers refused to start. I should have used a portable jump starter but it was in the boot so difficult to reach, (now kept in glove box). In the end I used a 12v battery and jumper cables that I thought I would never need again. So it powers up and I plug in and all seems right with it. On a whim I opened the boot and checcked around the battery in case there was a loose connection or suchlike. The battery was hot and so was the ground cable, so there was some serious current charging it, that DC-DC converter is capable of 1.8kw apparently. I shut down immediately and removed the battery. I was at least able to charge it nomally after but my 25 amp charger was working hard. I put the spare battery in temporarily although it doesn't really fit, and eventually put in a solar power system sealed battery that was half the price of the genuine item even though it was rated about the same. I had to use different cables but I had those anyway.
Lastly, there is a 30Amp fuse listed as IOD (Ignition Off Draw) in the main fuse box. It runs everything that needs to stay alive after shut down, WiFi server, Remote key receiver etc. and memory for aged fuel and range estimates apparently. Pulling that fuse has the same effect as disconnecting the battery ground and resets a few things. Useful when the fuel is older than three months and thar car says "Using Old Fuel" and won't go into parallel hybrid mode. Can't hurt to do that now and then.
