C30 NOx Sensor Failure

Yeah, I had something similar happen on my C30. Check engine light and the smell of exhaust were the main clues. Have you checked the sensor connections and wiring for any obvious damage or corrosion? It could save you a lot of hassle if it's just a loose wire.

Thanks for the tip! Where exactly should I be looking for these connections? Is it easily accessible, or do I need to dismantle half the engine bay?

It's kind of tucked away near the exhaust system, not the easiest to get to. Honestly, if you're smelling exhaust and the check engine light is on, it might be worth getting it checked out professionally. Could be more serious than just a loose connection. My issue ended up needing a bit more work than I initially thought, that set me back 95€.

Thanks a lot for the advice! I think I'll take it to a shop and have them take a look. Better safe than sorry when it comes to the exhaust system and emissions. I appreciate the heads-up about the potential cost!