BMW 8 Diesel: Cold Weather Issues & Power Loss Mystery

Hey there! I actually had a really similar issue with my 2016 BMW 7 Series diesel last winter. I'm a casual DIYer with some basic experience working on cars. This sounds exactly like what I dealt with, the symptoms match perfectly. In my case, it turned out to be a faulty connection at the fuel filter heater plug. The workshop found that the cable connection had corroded and wasn't making proper contact. After replacing the connector and wiring, it ran like new again. The whole thing cost me 95 Euro and fixed all those symptoms, the poor idle, sluggish performance, and high fuel consumption. Before you head to the shop though, could you share what specific error codes you're getting? Also, when did you last change your fuel filter? This info would help compare if it's the same issue I had. If you've got a BMW 8, you're probably already going to a BMW specialist, but if not, I'd really recommend one for this kind of problem.

Thanks for sharing your experience! My fuel filter was actually changed at my last service about 5,500 KM ago. I'm getting P0183 and P0184 codes. After what you mentioned about the connector issues, I checked under the hood and noticed some minor corrosion around the fuel filter heater connector, might be onto something there! Would be great to know if those were the same codes you got. The symptoms do sound identical. Hoping I can get away with just a connector replacement like you did, rather than the full heater assembly.

Hey again! Yes, those were exactly the same error codes I got with my BMW! That P0183 and P0184 combo is pretty much the smoking gun for fuel filter heater circuit issues. When I saw your codes, I was like "yep, been there!" After seeing you've got corrosion on the connector too, I'm even more convinced it's the same problem I had. And good news, since your fuel filter is pretty new, that's probably not the culprit. Just to add to my earlier experience, before I got it fixed, I noticed the problems were way worse on cold mornings. The engine would almost shake at idle until it warmed up. Fuel consumption went up by about 15-20% too. Really annoying stuff. Quick tip though, when they fix the connector, make sure they also check the wiring harness for any damage. In my case, there was a bit of wire fraying near the connector that they caught and fixed at the same time. Better to get it all sorted while they're in there. Really glad I could help point you in the right direction! Let me know how it goes when you get it fixed. These BMWs are great cars when everything's working right!

Thanks so much for all that detailed info! This has been super helpful. You're definitely right, the symptoms are exactly what I'm experiencing, especially that shaking idle in the morning. The matching error codes and the corrosion I found really seal the deal. I've gone ahead and booked it in at my local BMW specialist for next week. I'll make sure to mention the connector and wiring harness check specifically, based on your experience. Really hoping it'll be a straightforward fix like yours was. The thought of just needing a new connector rather than the entire heater assembly is such a relief! I'll probably report back here after it's fixed, might help someone else with the same issue down the line. These modern diesels are fantastic when they're running right, but when something's off, it can be tricky to diagnose. Thanks again for sharing your experience, it's saved me a lot of worry and probably some cash too!