BMW 6 Diesel Running Rough, Water Sensor Issue?

Hey there! I've got some experience working on cars, and I had a similar issue with my 2018 BMW 5 Series diesel. I feel your pain! When my check engine light came on, the engine was also running really rough. Turns out it was a faulty cable connection to one of the sensors. Took it to my regular workshop, and they diagnosed it pretty quickly. They found a damaged wire connection that was causing the sensor to give wrong readings. The fix was straightforward, they replaced the wiring harness and connections. Cost me 95 Euro, and the car's been running smooth ever since. Before I can share more specific advice, could you tell us: What error codes are you getting? Does the rough running happen more at idle or while driving? Have you noticed any changes in fuel consumption? I know the 6 Series pretty well, and these details would help pinpoint if you're dealing with the same issue I had.

Thanks for your detailed reply! Really appreciate you sharing your experience. I've got error codes P0204 and P0087 showing up. The rough running is definitely worse at idle, and yeah, I've noticed it's been drinking more fuel lately. Mine's at 126821 KM and just had its service last month, so this caught me off guard. The cable connection issue you mentioned sounds similar to what I might be experiencing. The engine particularly struggles first thing in the morning. Did yours do the same? I'll try getting it checked at the workshop this week. Just wanted to gather some insights from fellow BMW owners before heading in. Does anyone else have experience with these specific error codes in their diesel BMW?

Hey again! Thanks for providing those details about your 6er. Funny enough, when I had my issue, I was getting the exact same error codes! However, in my case, after further diagnosis, it turned out I was a bit too optimistic thinking it was just the wiring. The P0087 code (fuel rail pressure too low) combined with P0204 (injector circuit malfunction) pointed to a bigger problem with my fuel system. My car was doing the exact same thing, super rough in the morning and drinking fuel like crazy. The mechanic found that one of my fuel injectors was failing, and that's what was causing all these symptoms. The wiring was actually fine, but the injector itself was toast. Had to shell out quite a bit more than just the 95 Euro I mentioned before, ended up being around 800 for the new injector plus labor. But honestly, it was worth every penny because the car's been running like a dream since then. Given your description and those specific codes, I'd bet you're dealing with a similar injector issue. Definitely get it checked soon, running with a bad injector can cause more problems down the line. Let me know what your mechanic says! I'm really curious if it turns out to be the same problem.

Thanks so much for the follow-up and being honest about the actual repair costs! Was getting my hopes up with that initial 95 euro estimate, but I guess that's how it goes with these cars. The injector issue makes total sense given the symptoms. Actually feel a bit relieved knowing someone else has dealt with the exact same problem and got it sorted. I've got an appointment at the workshop tomorrow morning, and I'll definitely mention your experience with the injector failure. Really appreciate you taking the time to share all this info, it'll help me go in more informed and hopefully avoid any unnecessary diagnostic costs. I'll update the thread once I get it fixed, might help others with similar issues down the line. Thanks again for your help!