Z3 Check Engine Alert: Exhaust Sensor Mystery Solved

Hey there! I had a similar issue with my 2003 BMW Z4 last year. The symptoms were almost identical, check engine light, limp mode, and terrible fuel economy. Initially thought it was just the sensor, but when I took it to the garage, they found a crack in the exhaust manifold that was causing the sensor to read incorrectly. The leak was allowing extra air into the system, throwing off all the readings. The mechanic showed me that the manifold had developed hairline cracks near the joints, pretty common issue in these engines when they age. Since hot exhaust gases were escaping, the temperature sensor was getting false readings. It was definitely a serious repair job since leaving it unfixed would've kept damaging other components and killing the fuel economy. Had to get the manifold replaced along with the sensor and some gaskets. The car's been running like new since then, no more check engine light, power is back to normal, and fuel consumption returned to standard. Given your symptoms, I'd recommend getting it checked soon, as exhaust leaks only get worse over time.

Thanks for sharing your experience! That's really helpful info about the manifold issue. Out of curiosity, do you remember roughly how much you ended up paying for the whole repair? Also, has everything been running smoothly since the fix, or have you noticed any other problems popping up? I'm trying to get a better idea of what I might be looking at cost-wise with my Z3, and whether I should prepare for any related issues down the line.

Hey again! Just wanted to update you on my Z4 repair saga. Got it sorted last month and it was actually much simpler (and cheaper!) than my initial manifold problem fears. Turned out to be just a faulty exhaust temperature sensor and a small leak in the exhaust system. Total bill came to 265 €, way less painful than I expected! Since the fix, she's been running absolutely perfect. No more check engine light, power's back to normal, and fuel consumption is where it should be. Zero issues have popped up since then, which is a massive relief. The mechanic did a thorough job and explained everything they found. If your symptoms are similar to what mine were, you might be looking at the same kind of fix. It's definitely worth getting it checked out, these problems tend to cost more the longer you leave them. The peace of mind alone was worth every penny for me. Plus, better fuel economy means I'm actually saving money now compared to when it was running poorly! Hope this helps give you a better idea of what you might be dealing with. Let us know how it turns out!

Thanks everyone for your input! Just wanted to give you an update on my Z3 situation. Finally got the courage to visit a new mechanic yesterday, and I'm actually relieved I did! Turns out the issue wasn't as terrible as I feared. They found the faulty exhaust temp sensor and a small exhaust leak, pretty much what you described. The total repair came to around 300 bucks, which feels like a steal compared to what I was imagining. The interesting part was watching the mechanic at work. They were super transparent, even showed me the old sensor and where the leak was. They fixed everything in about three hours, and the difference in how the car runs now is like night and day! The check engine light's gone, got my power back, and the fuel gauge isn't dropping like a stone anymore. Really glad I asked here before going in, helped me feel more confident about what to expect. Sometimes you just need that little push to try a new mechanic, right? Guess my previous bad experience made me more nervous than I needed to be. Thanks again for all your help!