Hyundai i10 Fault Memory Lock Active

That sounds familiar. I had a similar issue with my old Opel Astra, though it was a diesel. "Fault memory lock active" usually means the ECU (Engine Control Unit) has detected a problem and locked the fault code to prevent it from being cleared easily. Undervoltage is a good starting point, since low voltage can cause all sorts of weird errors in modern cars. Have you checked your battery voltage recently? Was it sitting for a long time?

Yeah, the car was sitting in the garage for 3 weeks. Where exactly should I measure the voltage?

Okay, leaving it sitting for 3 weeks could definitely explain it. Measure the voltage directly at the battery terminals using a multimeter. You're looking for around 12.6 volts with the engine off. If it's significantly lower, that's likely your culprit. Given the error and your suspicion, it's probably best to take it to a workshop. They can properly diagnose the electrical system and clear the fault codes once the voltage issue is resolved. It’s not worth buying a very expensive diagnostic tool for just one old car.

Thanks, that's helpful. I'll get it checked out at the workshop. It cost me 240€ to fix the undervoltage issue and clear the code.