C1 Overvoltage and Battery Issues

Sounds like a headache. Overvoltage errors on a C1 often point to a charging issue. Have you checked the voltage regulator output? What voltage readings are you getting?

Where exactly is the voltage regulator located on the C1, and how would I go about testing it properly? I don't want to fry anything even more.

It's usually integrated into the alternator itself on those. Best bet is honestly to get it properly diagnosed at a workshop. Messing with it without the right tools or knowledge can cause more harm than good, especially with modern ECUs being sensitive.

Thanks for the advice. Took it to a shop and you were right. Turns out the battery was indeed the culprit, causing overvoltage and frying the circuit protection. New battery and diagnostics cost me 290€, but at least it's fixed!