M Klasse engine light and exhaust issues

I had a similar experience with my M Klasse. The engine light, rough running, and exhaust smell point towards the lambda sensor, but don't rule out the catalytic converter. It's like having a blocked artery; the sensor might be reporting the problem accurately, but the converter itself could be the source. Have you checked the condition of your catalytic converter?

Thanks for the quick reply. How can I assess the catalytic converter's condition without special equipment? Is there a test or visual inspection I can do? Were your symptoms identical to mine, including the rough running and strong exhaust odor?

Yes, my symptoms were almost identical. Checking the catalytic converter without diagnostic tools is tricky. You might hear rattling from inside it, suggesting a breakdown. Given your symptoms and my experience, I'd recommend a workshop visit. They can properly diagnose it, and misdiagnosing it yourself can cost more than the workshop fees.

I appreciate the advice. The blocked artery analogy was helpful. I scheduled an appointment with a trusted workshop. It was a defective lambda sensor, as suspected. The replacement and a minor exhaust repair for the leak cost 380€. Thanks for the guidance.