BMW 8 Diesel Nightmare: Glow Plug Drama & Failed Tests

Hey there! I have some experience working on cars and had a similar issue with my 2017 BMW 7 Series diesel last winter. When I read your post, it immediately reminded me of what I went through with mine! Had the exact same symptoms, difficult cold starts, warning lights, and that annoying constant preheat light. Took it to my trusted workshop, and turns out it was indeed a faulty connection in the glow plug wiring harness. The repair was fairly straightforward, they had to replace some corroded wiring and a connector. Cost me 95 Euro and the car's been running perfectly since then. Before we jump to conclusions though, could you share: How many miles/kilometers on your car? Are you getting any specific error codes? When exactly did these symptoms start? I've also owned a BMW 5 Series before, and these symptoms can sometimes point to other issues, so having more details would help narrow things down.

Thanks for the detailed response! My BMW has 151930 KM on the clock and had its last service about 2 months ago. I'm getting error code P0380 consistently. The symptoms started about three weeks ago when temperatures dropped. Initially, it was just occasional rough starts, but now it's becoming more frequent. The mechanic did a diagnostic scan which showed glow plug circuit malfunction, but I wanted to get some real-world experience from other owners before committing to repairs. Your experience sounds very similar to what I'm dealing with. Did you notice any improvement in fuel consumption after the repair? The smoke during acceleration is really starting to worry me.

Hey again! Yes, absolutely, after reading about your mileage and error code, I'm even more convinced it's similar to what I experienced with my BMW. And funny you should ask about the fuel consumption, that was actually one of the most noticeable improvements after the repair! My car was drinking fuel like crazy before the fix, but it went back to normal right after. The P0380 code is exactly what I had too. The smoke during acceleration was really worrying me as well, I remember being embarrassed every time I pulled away from a stop because of that gray cloud behind me. But it all cleared up after the wiring repair. Quick tip from my experience, while they're in there fixing the wiring, have them check the glow plugs themselves too. In my case, two of them were pretty worn out, so I had those replaced at the same time. It wasn't much extra work since they were already accessing that area, and it gave me peace of mind knowing everything in the system was fresh and working properly. Trust me, don't wait too long on this repair. The longer you drive it with these symptoms, the more strain you're putting on other components. I learned that the hard way with my old 5 Series years ago!

Hey thanks so much for all the info and advice! I really appreciate you sharing your experience, especially since it matches my situation so closely. I've decided to book my car in next week and will definitely have them check the glow plugs while they're at it, that's a really smart suggestion. The fuel consumption and smoke issues are getting worse by the day, and you're right about not wanting to risk damaging other components. Even though the repair cost might sting a bit, it sounds like it'll be worth it to get everything sorted properly. I'll make sure to get that wiring harness checked first since that seems to be the most likely culprit based on your experience. Seriously, thanks for taking the time to help out, it's really put my mind at ease knowing there's likely a straightforward fix for all these symptoms. Will let you know how it goes after the repair!