NOx Catalyst Issues? Get Expert Diagnostic Help Here

Had a similar issue with my 2017 Chevy Cruze last year, also faced emissions system troubles with the check engine light. As someone with basic car repair experience, I first noticed a slight performance drop and higher fuel consumption. The workshop diagnosed a leak in the exhaust system right before the NOx catalyst. The entire repair, including parts and labor, cost me 265 Euro, they had to replace a cracked section of the exhaust pipe and reseal some connections. The NOx catalyst itself was actually fine, which was a relief since those are much pricier. What's your current mileage and are you noticing any specific symptoms like: Louder than normal exhaust noise? Decreased fuel efficiency? Rough idling? Sulfur-like smell? Share those details and the specific error codes you're getting, it'll help narrow down whether you're dealing with the same issue I had.

Thanks for the detailed response. Currently at 48139 KM and definitely noticing similar symptoms, getting worse fuel efficiency and there's a noticeable sulfur smell, especially when idling. Getting error codes P0420 and P0430. Just had service done last month but they didn't catch this issue. The exhaust noise isn't super loud but there's a subtle rattling that wasn't there before. Been monitoring my fuel consumption and it's jumped up about 15% in the last few weeks. Given that NOx emissions and air quality standards are pretty strict these days, I'm worried this might be a bigger issue than just a simple exhaust leak. Did your repair completely resolve the fuel efficiency issues?

Yeah, those P0420 and P0430 codes match exactly what I dealt with on my Cruze. After my repair, the fuel efficiency went right back to normal within about a tank or two of gas. That sulfur smell you're getting is a classic sign of exhaust leakage, had the same thing and it drove me nuts. The reason I mention this is because my catalytic converter was actually fine, it was just getting bad readings from the exhaust leak. The NOx emissions system was throwing those codes because the sensors weren't getting accurate readings due to the leak. Once they fixed the exhaust system leak, all my symptoms cleared up. Here's what's interesting, with similar mileage to yours, what looked like catalyst aging turned out to be just a cracked exhaust pipe near the flex joint. The automotive repair shop first suspected a failing catalytic converter, but a proper smoke test revealed the actual leak point. If you're noticing the same symptoms I had, especially that sulfur smell and rattling, I'd bet you're dealing with a similar exhaust system issue rather than a failing NOx storage catalyst. Would definitely recommend getting a smoke test done before replacing any major components, could save you a bunch of money.

Thanks for the thorough explanation, this definitely sounds like what I'm experiencing. Going to take it in for that smoke test next week to check the exhaust system first. The car diagnostics pointing to a possible exhaust leak rather than a full NOx catalyst failure is actually a relief, especially cost-wise. I'll make sure to ask them specifically about checking around the flex joint area since that's where your leak was found. Makes total sense about the sensors getting bad readings due to the leak, would explain why the fuel efficiency tanked and those error codes popped up. The fact that your repair completely fixed both the emissions issues and fuel consumption gives me hope this won't be a major repair. Will update once I get the smoke test results and find out exactly what's causing these NOx emissions problems. Thanks for helping me avoid potentially replacing parts that might not actually need replacing.