BMW 6 Diesel Running Rich: O2 Sensor Warning Signs

Hey there! I had a very similar issue with my 2016 BMW 5 Series 520d last month. The symptoms matched yours, check engine light and terrible fuel economy. Turned out the oxygen sensor wasn't the culprit in my case, it was actually a loose wiring connection to the mass airflow sensor. The mechanic showed me where the cable insulation had worn down, causing intermittent connection issues. While the repair wasn't too complicated, ignoring it could have led to serious engine performance problems and potential damage to the catalytic converter. The fix involved replacing the damaged wiring harness and securing the connections properly. The car's been running perfectly since then, back to normal fuel consumption and no warning lights. Worth getting it checked soon, electrical issues with sensors can get worse if left unattended. Just make sure whoever looks at it has experience with BMW diesel engines, as the diagnostic process needs to be thorough. Hope this helps.

Thanks for sharing your experience! That's really interesting about the wiring harness, never would've thought that could cause similar symptoms. Could you tell me roughly how much you ended up paying for the repair? Also, has everything stayed problem-free since the fix, or have you noticed any other quirks? Always good to know what to watch out for with these engines.

Hey again! Just wanted to update you on my situation. After seeing your message, I actually went ahead and got my car checked at a BMW specialist. Turns out my initial experience with the wiring wasn't the full story, they found that the aged oxygen sensor was indeed playing up too! They fixed both issues, and it cost me 95 € for sorting out the cable connection problem. I've been keeping a close eye on things since the repair about three weeks ago, and honestly, it's running like a dream. Fuel consumption is back to normal, and that annoying check engine light hasn't made a reappearance. The car feels much more responsive too, which is a nice bonus. These BMWs can be tricky beasts, but getting the right mechanic makes all the difference. In my case, fixing both the wiring and the O2 sensor was definitely worth it. Haven't noticed any other issues since then, touch wood! If you're still hesitating about getting yours checked, I'd say go for it. Better to catch these things early before they cause bigger problems. Let me know if you need any more details about the repair, happy to help!

Thanks for the detailed follow-up! I finally took your advice and brought my car to a certified BMW specialist last week. You won't believe it, they found both a faulty oxygen sensor AND some damaged wiring! I'm actually relieved I didn't try fixing it myself. The mechanic was great, showed me exactly what was wrong and explained everything clearly. The whole repair took about 3 hours, and while it wasn't cheap, the difference in how the car runs now is like night and day. The fuel consumption has dropped back to normal, and that pesky check engine light is finally gone. The engine feels smoother too, guess those sensors really do make a big difference. I'm just glad I didn't wait any longer to get it checked out. My previous bad experience with mechanics made me hesitate, but this specialist really knew his stuff. Definitely learned my lesson about finding the right mechanic for these German engines. Thanks again for sharing your experience, it gave me the push I needed to get this sorted!