Seat Arosa Overheating Issue

Sounds like you're having active air flap issues. I had a similar problem with my Opel astra. The fault code indicated a problem with the grille shutter. I'd check the wiring and the connector first, but it's likely the electromechanism itself. Is your cooling system performing as expected? What fault codes are you getting?

Grille shutter? Electromechanism? Fault codes? I'm not sure what those are. Where can I find the fault codes? And what exactly is the electromechanism doing?

The grille shutter is part of the active air flap system, it's in front of the radiator. The electromechanism is the motor that controls it. The fault code is a diagnostic trouble code stored in the car's computer. You'd need an OBD2 scanner to read it. Given the car overheating, and the likely cause being a faulty electromechanism, I'd recommend you take it to a workshop. If they confirm it, 590€ sounds about right for that kind of repair.

Thank you so much for your help! I took it to a workshop and they confirmed it was the active air flap electromechanism. The repair cost was exactly as predicted, around 590€. Now it's fixed!