XC40 Overheating Coolant Leak

Sounds frustrating! Similar problem with my old Renault Megane, though the symptoms weren't exactly the same. I was getting random error messages and the car would occasionally go into limp mode. Turned out to be a faulty CAN bus connection. Have you checked the wiring and connectors to the ECU? Sometimes a loose or corroded connection can cause all sorts of weird issues.

Thanks for the insight! I'm not very experienced with car electrics, so where exactly should I look for the ECU and these connections? Is it something I can easily check myself, or is it best left to a professional?

If you're not comfortable with car electrics, I'd strongly advise against poking around too much. The ECU is usually located in the engine bay or under the dashboard, but it varies from car to car. Best bet is to get it to a workshop with proper diagnostic tools. They can pinpoint the exact fault and fix it properly. Save yourself a headache!

Thanks again for your advice! I took it to the workshop, and you were right – it was a defective cable connection to a control unit. The final repair cost was 95€. Problem solved!