Seat Formentor Overheating and Check Engine Light

That sounds suspiciously like a connectivity issue I experienced with my old Volvo. The symptoms are bang on. Check engine light, overheating, coolant loss... Does the engine seem to be running rough, too? In my case, it turned out to be a faulty data link between the ECU and the temperature sensor. Is the car throwing any specific error codes during diagnostics? A common communication fault can manifest in a number of ways, seemingly unrelated. You need to check the wiring harness and connectors related to the engine control unit. Corrosion or loose connections are often the culprits. Have you checked the basics, like battery voltage and ground connections? A low voltage can sometimes cause spurious errors in the control system.

Rough running, yes a little! Error codes... there were loads, the garage just said 'control unit communication error'. Data link... where exactly is that? And the wiring harness, is that easy to get to?

Ah, 'control unit communication error' – that's a broad stroke. In my Volvo's case, the data link was part of the wiring loom near the thermostat housing. Honestly, unless you're comfortable with car diagnostics and electrical systems, I'd advise against poking around too much. You could make things worse. It's probably best to have a workshop investigate the car diagnostics. Do you concur with the diagnosis: 'Cable or plug connection of the component defective'?

Just wanted to let you know, got it sorted! Turns out it was a dodgy connection like you said. 95€ later and she's purring again. Thanks a million for your help!