GLK NOx Sensor Issue and Exhaust Smell

Interesting. I had a similar issue with my GLK, although I didn't notice an exhaust leak. The check engine light and NOx sensor code were definitely present. Did you check the sensor's wiring harness and plug? Sometimes a loose or corroded connection can trigger the error. It's a relatively cheap fix if that's the culprit, but if the sensor itself is bad, you're looking at a more expensive repair. I'd be concerned about the catalytic converter too, as prolonged issues with the air-fuel ratio can damage it. Is it a diesel engine?

Thanks for the quick reply! You mentioned checking the wiring harness and plug. Do you recall specifically where that connection is located? I've visually inspected around the sensor itself, but I didn't see anything obviously broken or loose. Also, to confirm, my GLK has a gasoline engine, not a diesel engine. I'm just trying to understand the potential impact on the catalytic converter and the pollution control in general.

Okay, gasoline engine, that's good to know. Diesel engines have their own quirks when it comes to NOx sensors. As for the connector location, it's usually pretty close to the sensor itself, maybe tucked up a bit higher on the exhaust system. Honestly, if you're smelling exhaust and you're not completely comfortable troubleshooting the wiring, I'd take it to a trusted workshop. They can smoke test for leaks and properly diagnose the NOx sensor and its wiring. A faulty NOx sensor can definitely mess with your air-fuel ratio and could, eventually, damage the catalytic converter. It's better to be safe than sorry when it comes to pollution control.

I followed your advice and took it to a workshop. Turns out it was a damaged wire going to the NOx sensor, just like you suspected! They repaired the connection, cleared the code, and the exhaust smell is gone. Total cost was indeed close to 95€. Thanks for the help!