G Klasse rough running and exhaust smell

I have observed similar symptoms in my G Klasse. An exhaust leak can certainly affect the lambda sensor readings, potentially triggering the engine light and causing rough running. Have you inspected the exhaust pipe for any visible damage or corrosion? It would also be prudent to check the condition of the catalytic converter.

I did a quick visual inspection of the exhaust pipe and noticed some corrosion, but nothing major. Is it possible for a small exhaust leak to cause all these issues, including the rough running and the engine light? Also, where are the NOx sensors located, and how difficult are they to replace?

A seemingly small exhaust leak prior to the catalytic converter can indeed cause significant issues. It disrupts the oxygen sensor readings, leading to incorrect fuel mixture and rough engine performance. Regarding the NOx sensors, their location can vary, but they are typically situated downstream of the catalytic converter. Replacement can be complex, potentially requiring specialized tools. Given your symptoms and the potential for affecting lambda sensor behavior, I would recommend consulting a qualified technician for a proper diagnosis.

I took it to a workshop. Turns out it was indeed a defective lambda sensor and a small crack in the exhaust pipe right before the catalytic converter. They replaced the sensor and patched the exhaust pipe. Total cost was 375€. Runs much better now. Appreciate the help!