Seat Ateca Oxygen Sensor Problem

That sounds familiar. I had a similar check engine light situation with my Opel Insignia. It also turned out to be a faulty sensor in the exhaust system. Have you checked the sensor's wiring and connections yourself? Sometimes it's just a loose plug.

I haven't checked the wiring myself. Where exactly is the oxygen sensor located? Is it easily accessible, or do I need special tools?

The oxygen sensor is usually located in the exhaust system, before or after the catalytic converter. It might be tricky to reach without lifting the car. Given the higher fuel consumption, and the check engine light, and the risk of damaging vehicle emissions components, I suggest having a workshop take a look. They can properly diagnose the issue.

Thanks for the help. I took it to a workshop, and it was indeed a faulty sensor, as suspected. The cable and plug connections were fine, so they replaced the sensor. The check engine light is off now, and the vehicle emissions seem normal. Repair cost was 95€.