Mercedes C Klasse Oxygen Sensor Issues and Fuel Consumption

I had a similar issue with my C Klasse. The oxygen sensor heater element can fail. Have you checked the exhaust system for any visible damage or leaks? A faulty oxygen sensor can definitely cause the check engine light to appear and increase fuel consumption. Is it only happening at certain times or constantly?

I haven't seen any visible damage to the exhaust system. The error and increased consumption are always present. Where is the oxygen sensor located? I want to inspect the car components and the cable or plug connection myself.

It's located in the exhaust system, before or after the catalytic converter. I would recommend getting it checked out in a workshop. It could be the sensor itself or a defective cable or plug connection as you suspected. In my case, it was the sensor, and the error memory showed the same error.

Thanks for the information. I took it to a workshop and you were right. It was the oxygen sensor. The repair cost me 95€. Now everything is working fine again.