Subaru NOx Sensor Failure: Repair Tips and Costs

Had the same issue on my 2012 Subaru Legacy with the gasoline engine. The check engine light triggered due to a faulty connection between the emission sensor and the main wiring harness. Initially suspected catalytic converter problems due to the exhaust fumes, but diagnostic testing revealed it was just corroded wiring. The repair involved cleaning the connector pins and replacing the damaged section of the wiring harness that connects to the NOx sensor. This fixed both the sensor readings and the exhaust fume issue. The job took about 2 hours of labor and was not a major repair. For correct diagnosis, make sure they test both the sensor functionality and check all cable connections, as symptoms can be similar. A faulty connection can mimic a bad sensor reading while being much simpler to fix. The pollution control system on these models is generally reliable, just needs proper maintenance. Would recommend getting a second opinion before replacing any parts, as corrupt connections are common in this age range of Subarus and often mistaken for sensor failure.

Thanks for sharing your Legacy repair experience. Your wiring issue sounds exactly like what I experienced with my Exiga. Got the same symptoms with the check engine warning and exhaust problems, though mine turned out to be a completely failed NOx sensor rather than just wiring. Wondering how the repair has held up for you since then? Also, could you share what the final cost was for your wiring fix? Would help me gauge if the quote I got for a full sensor replacement is reasonable.

Thanks for asking about the follow-up on my Legacy repair. The wiring fix has worked perfectly since seeing the mechanic, no more emission sensor warnings or exhaust system issues. The nitrogen oxide readings are now spot-on, and the check engine light has stayed off. The total repair came to 95€, which covered cleaning and fixing the cable connection to the NOx sensor. This was significantly cheaper than a full sensor replacement. The catalytic converter and rest of the pollution control system have been working flawlessly since the repair. If you are getting quotes for a complete sensor replacement, expect to pay quite a bit more than what I did for just the wiring repair. However, if your diagnostic tests confirm a failed sensor rather than just connection issues, then replacement might be your only option. The key is getting accurate diagnosis upfront, as replacing parts unnecessarily can get expensive fast.

I took your advice and got my Exiga checked at a different mechanic. Turned out my NOx sensor was completely dead, affecting the air-fuel ratio and causing those exhaust fumes. The new mechanic was thorough and tested all connections first before confirming the sensor failure. Ended up paying 380€ for the full sensor replacement including labor. More than your wiring fix but the service was excellent. They showed me the old sensor and explained how it impacted the exhaust system performance. The catalytic converter thankfully wasnt affected. After the repair my engine runs much smoother and the check engine light hasnt come back on. The pollution control system is working properly now and theres no more excess fumes. Really glad I got that second opinion you suggested, saved me from going back to the first mechanic who wanted to replace multiple parts unnecessarily.