BMW X4 Diesel Starting Issues, Cold Start & Power Problems

Hey there! I've had some experience with cars, and your symptoms sound familiar. I actually dealt with something very similar on my 2019 BMW X3 diesel last winter. I'd noticed the same issues, hard cold starts, rough idle, and that annoying power loss. Took it to my regular workshop where they found it was indeed a faulty connection in the fuel heater wiring harness. The cable had gotten corroded and wasn't making proper contact. They replaced the connection and cleaned up the whole assembly, cost me 95 Euro and fixed all those symptoms. Before I can give more specific advice, could you share: How many miles/kilometers on your X4? Have you checked if there are any error codes? When was your last fuel filter change? If you want, I could share more details about my experience with both the X3 and X5 (I've worked on both). These BMWs can be a bit tricky with their diesel systems, but usually it's nothing major.

Thanks for reaching out! Just had my service done last month at 135619 KM, and I'm getting similar symptoms. Had the mechanic scan it and got P0148 and P0087 codes. The fuel filter was actually changed during the service, so I don't think that's the culprit. After reading about your experience, I'm starting to think it might be the same wiring issue you mentioned. These diesel systems can be quite sensitive to electrical problems. Did your workshop mention how they spotted the corroded connection? I might ask mine to take a closer look at that specific area. The symptoms match up perfectly with what you described.

Hey again! Thanks for sharing those details. Yeah, those error codes (P0148 and P0087) are exactly what I got with my X3 too, they're typically related to fuel pressure control issues. When my workshop diagnosed it, they actually did a systematic check of the entire fuel heating system. They found the corroded connection by doing a visual inspection and resistance test of the wiring harness, it was pretty obvious once they knew where to look. The connection was all greenish and crusty near the heater unit. Since you've already had your fuel filter changed, I'm even more convinced it's the same electrical issue I had. My mechanic mentioned these connections are kind of in a vulnerable spot where moisture can build up over time. After they fixed mine, all those annoying symptoms disappeared completely, cold starts became smooth, idle evened out, and my fuel consumption went back to normal. I'd definitely recommend having them check the wiring harness and connections specifically. The fix itself isn't complicated, but finding the exact spot can be tricky if they don't know what they're looking for. If you want, I can share the exact repair report from my fix, might help your mechanic zero in on the problem faster. Just make sure they do a proper inspection of all the connections, not just a quick look. When they fixed mine, they also applied some protective coating to prevent future corrosion, might be worth asking about that too.

Thanks so much for all the detailed info! It's really helpful to hear from someone who's been through the exact same thing. I've just called my workshop and mentioned the wiring harness issue you described, especially about checking those connections near the heater unit. They seemed pretty interested when I mentioned the protective coating too. Got an appointment booked for tomorrow morning. I'll make sure they do that resistance test you mentioned and check for any corrosion. Honestly, I'm feeling much more confident now knowing what to ask them to look for. Can't believe it might be something as simple as a corroded connection causing all these problems! I'll definitely let you know how it goes. Really appreciate you taking the time to share your experience in such detail. Hopefully, I'll be back to smooth starts and normal fuel consumption soon!