XC40 High-Voltage System Error

That sounds pretty rough. Is it showing as an error in the system memory too? Have you noticed if it happens more when the battery is low, or after a long drive maybe? Could be a battery issue, or something with the electrical wiring itself. But without proper diagnostics, it's hard to say for sure.

Good point about the battery! I hadn't really paid attention to when it happens. How would I check the high-voltage battery? Is that something I can even do myself, or does it need special tools?

Checking a high-voltage battery isn't like checking the battery in your old car. It could be a heavily discharged battery, or even a defective one, but it's also possible it's the inverter acting up. Either way, fiddling with EV systems can be dangerous. I would suggest going to a workshop. I suspect an electrical fault. It's better to be safe than sorry!

Thanks so much for the advice! I took it to a mechanic, and you were right – it turned out to be a problem with the high-voltage battery, caused by a defective cell. They replaced it, and the error is gone. Cost me around 290€, but at least it's fixed!