BMW Z3 NOx Sensor Failure: Fix Costs & Experiences?

Actually, I had a similar problem with my 2005 BMW Z4 last month. The NOx sensor issue came up along with the check engine light. From my garage visit, I can tell you it wasn't just the sensor, there was a corroded wiring harness connected to the NOx sensor, and the connector was pretty much shot. For me, it turned out to be more serious than initially thought. The exhaust leak was coming from a cracked manifold, which was putting extra stress on the sensor system. The mechanic showed me how the old wiring was completely degraded from heat exposure. They had to replace both the sensor and the wiring harness, plus fix the exhaust leak. You might want to get this checked soon because these issues can cascade into bigger problems with the emission control system. Just my experience, but make sure they inspect the whole exhaust system when you take it in, not just the sensor itself.

Thanks for sharing that, it's really helpful to know about the wiring harness and manifold issues you ran into. I'm starting to think my problem might be similar to yours, especially with the exhaust leak. Do you remember roughly how much you ended up paying for all the repairs? Also, has everything been running smoothly since the fix, or have you noticed any other problems cropping up?

Hey there! Glad to give you a follow-up about my Z4's NOx sensor situation. Actually, I got really lucky, turned out my issue was much simpler than I initially thought. When I took it to the mechanic, they found it was just a faulty cable connection to the NOx sensor. They fixed the plug connection for 95 €, and honestly, it's been running like a charm ever since. I know in my first reply I was worried about the wiring harness and manifold, but thankfully none of that needed replacing. The check engine light cleared up right after the repair, and I haven't had any emission problems since. The exhaust system is working perfectly now. It's such a relief when these things turn out to be simpler fixes, isn't it? My car's been performing great for the past few weeks, no warning lights, no strange noises, nothing. Honestly, I feel a bit silly now for expecting the worst, but you know how it goes with these older BMWs, you always fear the expensive repairs! Let me know how yours turns out, hopefully you'll get lucky with a simple fix too!

What a relief to hear your repair was so straightforward! After reading your previous message, I was bracing myself for a huge repair bill. I actually just got back from a mechanic I found through a car enthusiast forum. Turns out my issue wasn't too bad either! They found a small crack in the exhaust pipe near the sensor, which was causing the funky readings. The whole thing, including the new sensor and patching the exhaust, came to about 300 bucks. Way less than I was expecting! The funny part is, I spent weeks worrying about this, putting off going to a mechanic because of my last bad experience. But this new guy was great, showed me exactly what was wrong and fixed it on the spot. Car's running smooth now, no more check engine light, and it passed emissions with flying colors. Thanks again for sharing your experience, it really helped me get over my hesitation about taking it in. Sometimes these BMW problems aren't as scary as we think they'll be!