Seat Toledo oxygen sensor heater failure

Sounds like the dreaded oxygen sensor heater failure! I had a similar issue with my old Renault Megane. The check engine light kept popping up, and the fuel consumption went through the roof. Have you checked the wiring and the plug connection to the sensor? That was the culprit in my case.

Wiring and plug connection, you say? Is there a specific area I should be looking at, or is it just a general visual inspection?

It's worth checking the connection first. Give the plug a wiggle, see if it's loose or corroded. If it looks okay, I'd just take it to a workshop. Could be a faulty sensor itself, but a dodgy connection is more common. Is it worth getting your hands dirty?

Thanks so much for the help! It turned out to be a faulty connection, just like you suspected. 95€ later, and the malfunction indicator is finally off!