Mercedes M Klasse Diesel Oxygen Sensor Issue

I had a similar issue with my Mercedes C Klasse. The oxygen sensor, also called a lambda sensor, monitors oxygen levels in the exhaust. The heater element helps it reach operating temperature quickly, especially during cold starts. If it fails, the sensor won't function properly, triggering the check engine light, also known as the malfunction indicator lamp. The error code is likely related to the heater circuit. Check and clean the connection first. Do you know which oxygen sensor is reporting the fault? There are usually two: one before and one after the catalytic converter.

Good point about identifying the faulty sensor. I'm not sure which one it is. Is there a way to tell without taking it to a shop?

The error code should indicate which sensor is causing the problem. A generic OBD2 scanner might provide enough detail, or a Mercedes-specific diagnostic tool will pinpoint it exactly. If unsure, it might be best to take it to a workshop. They can quickly identify the faulty sensor, confirm the wiring, and replace the sensor if needed.

Thanks for the advice. I took it to a workshop. They confirmed it was a faulty oxygen sensor, and the wiring was fine. Replacing the sensor resolved the issue. Appreciate the help!