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Mercedes SLC NOx Sensor Issue

My 2017 Mercedes SLC with a gasoline engine is throwing a check engine light. I pulled the codes and it's pointing to a NOx sensor failure. Mileage is at 146568 km. Besides the light, I can also smell exhaust fumes, which is new. I'm thinking it might just be a bad connection, maybe a faulty plug on the sensor itself. Anyone else run into this? What am I looking at in terms of fixing this pollution control issue?

A 2017 Mercedes SLC owner experienced a check engine light and exhaust fumes, with diagnostic codes indicating a NOx sensor failure. The initial suspicion was a bad connection or faulty plug, but after cleaning the connections and further inspection, the issue persisted. The problem was resolved by replacing the faulty NOx sensor, which eliminated the exhaust smell and turned off the check engine light.

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4 comment(s)

Whoa, NOx sensor problems are the WORST! I had something similar happen on my SLC (don't remember the exact year). That smell of exhaust is definitely not a good sign. When you say 'bad connection' are you talking about visually inspecting the wires and the connector itself? Are you getting any specific error codes related to the sensor's signal or voltage? Because if it's a simple connection issue, you might be able to save yourself a ton of money.

Yeah, I did a quick visual. Didn't see anything immediately obvious, but I didn't get under the car for a super thorough look. I'll check for specific codes tomorrow. Just curious if your emission sensor issue was actually the sensor, or something else upstream.

Okay, so I remember now, the code was something like 'Nitrogen Oxide sensor circuit range/performance'. I messed around with it for a bit, but honestly, I'm not a mechanic. Ended up taking it to a workshop, and they found a loose wire. They charged me like 95€ to fix it. Probably worth getting it checked out if you're smelling exhaust though. Could be more than just the sensor failing.

Appreciate the info. Got the specific codes today and they were all NOx sensor related. Gave the connections a proper cleaning and still no luck. Bit the bullet and took it to my local mechanic. Turns out the sensor itself was bad. Replaced it and the exhaust smell is gone and the check engine light is off. Thanks again for the help!

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MERCEDES

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SLC