G37 Secondary Air Valve Issues Smell & MPG Problems?

Hey there! I had a similar issue with my 2015 Infiniti Q50 (I have some experience working on cars, but I mostly trust my mechanic for complex issues). The symptoms you're describing sound exactly like what I dealt with check engine light, bad MPG, and that nasty exhaust smell. Took it to my trusted workshop last year, and it turned out to be a faulty electric switching valve. Cost me around 140 Euro to fix, including labor. After replacing it, all problems disappeared immediately. What's your exact model and engine size? That would help me share more specific details about the repair process. Also, have you scanned for error codes? Those would be really helpful to confirm if we're dealing with the same issue. Just curious is your car completely stock, or have you done any modifications to the exhaust system?

Thanks for sharing your experience! I'm at 107945 KM and just had my service last month. That's really helpful info about the switching valve sounds spot on with what I'm experiencing. I haven't done any mods, keeping it stock to avoid any warranty issues. Haven't grabbed the error codes yet, but planning to swing by a workshop tomorrow to get them checked. The cost you mentioned seems pretty reasonable compared to what I was worried about. It's the 3.7L V6 model. Did you notice any performance changes after the repair?

Hey again! Yeah, after fixing that switching valve on my Q50 (also with the 3.7L V6), I definitely noticed some improvements. The biggest change was in fuel economy went from burning through gas like crazy back to normal consumption. Performance-wise, it felt smoother, especially during cold starts. Since you mentioned you're at 107945 KM, that's actually pretty close to when mine started acting up (around 115000 KM). These valves tend to give out around this mileage from what my mechanic told me. One thing I forgot to mention in my first reply after the repair, that annoying exhaust smell completely disappeared. It was such a relief! Good call on getting those codes checked at a workshop. When I got mine scanned, it showed P0411, which pointed straight to the secondary air system. If you get the same code, you're probably looking at the same issue I had. Let us know what codes you get! If it's the same problem, at least you know it's a pretty straightforward fix. My car's been running great since the repair, no issues whatsoever for the past year.

Thanks so much for all the detailed info! It's super reassuring to hear your car's been running great after the fix. I'm actually feeling a lot better about this whole situation now was worried it might be something way more serious (and expensive!). Will definitely post the error codes here once I get them checked tomorrow. Really appreciate you taking the time to share your experience, especially since you've got the same engine. Fingers crossed it's just the switching valve like yours was. It's good to know the repair made such a noticeable difference in both the fuel economy and performance. Thanks again for the help!