BMW X7 Diesel: Glow Plug Nightmare Needs Fixing

Hey there! I had similar issues with my 2017 BMW X5 Diesel. I'm a DIY enthusiast with some experience working on cars, though I usually leave the complex stuff to professionals. My symptoms were pretty much identical, preheating light wouldn't go off, hard starts in cold weather, and black smoke. Took it to my trusted workshop and turns out the wiring harness connecting to the glow plug control module was damaged. Some connectors were corroded, causing poor contact. Total fix was 95 Euro for parts and labor. Since you've got the X7, which runs on a similar engine platform as my old X5, it might be the same issue. However, before jumping to conclusions, could you share: Current mileage? Any diagnostic codes you've pulled? When did the symptoms first appear? It might save you some cash if you can pinpoint the exact problem before heading to the shop.

Hi, thanks for sharing your experience! My X7 has 176828 KM on the clock, and symptoms started about 2 weeks after my latest service. I'm getting P0380 code (glow plug/heater circuit malfunction). Haven't pulled any other codes yet. Your wiring harness issue sounds similar to what I'm experiencing. I'll definitely have the connections checked first before replacing the entire glow control module. Really appreciate the heads-up about checking the connectors, could save me a bunch of money if that's all it is. Did you notice if yours was running rough at idle too? Mine seems to have a slight vibration that wasn't there before these issues started.

Hey, glad to help! Yeah, I remember my X5 actually did have a rough idle too, I forgot to mention that in my first response. It's interesting you mention the timing of your symptoms showing up after the service. My issues also appeared shortly after routine maintenance, which makes me even more convinced we're dealing with the same problem. The P0380 code is exactly what I got too! With the similar mileage (mine had around 165000 KM when this happened), it's really pointing to the wiring harness issue. The vibration at idle is typically what happens when not all glow plugs are firing properly due to poor connections. Quick tip from my experience, when my mechanic was fixing it, he found that the connector pins were slightly bent, probably from the last time someone worked on it. This was causing intermittent contact issues. Make sure whoever checks yours takes a good look at the pin alignment too. Also, watch out for moisture in the connectors, that was contributing to my corrosion problem. My mechanic applied some dielectric grease after cleaning everything up, and I haven't had any issues since then. Might be worth asking your mechanic to do the same if they find similar issues.

Thanks for the detailed insight! You've actually helped me narrow down what to look for. Knowing that your X5 had that idle vibration too makes me feel better about my diagnosis. I'm definitely going to get those connectors checked first before jumping into more expensive repairs. I'll ask my mechanic to specifically inspect the pin alignment and check for moisture damage. The dielectric grease tip is really helpful, wouldn't have thought of that. Seems like these connector issues are a bit of a common problem with our BMW diesels after they rack up some miles. Really glad I asked here before heading to the dealer, who probably would've jumped straight to replacing the whole glow control module. Will update once I get it sorted out. Thanks again for taking the time to share your experience, super helpful!