BMW X7 Diesel Glow Plug Warning: Cold Start Nightmare

Had the same issue with my 2020 BMW X5 diesel last winter. The symptoms you're describing match exactly what I experienced, glow plug warning, check engine light, hard starts, and black smoke. At the garage, they diagnosed a faulty glow plug control module and damaged wiring harness. Two of the glow plugs were completely dead, and the connection to the control unit was corroded. The smoke was coming from incomplete combustion due to the failing pre-heat system. It was a serious job because they had to remove several components to access the harness and module. Took them about 6 hours to complete everything. Since the repair, the car starts perfectly in cold weather, and there's no more black smoke. You're right to suspect the preheating control unit. Based on my experience, I'd say get it checked soon before it potentially causes more damage to your engine. The sooner you address it, the better.

Thanks for sharing your experience! It's really helpful to know I'm not alone with this issue. Your X5's symptoms sound identical to what I'm dealing with on my X7. Quick question, do you remember roughly how much the whole repair set you back? Also, has everything been running smoothly since the fix, or have you noticed any other issues pop up? Just trying to get an idea of what I'm in for, both cost-wise and reliability-wise. Cheers!

Hey there again! Just wanted to follow up on my previous reply. I actually got my X5 fixed last week, and it was way less complicated than my initial repair experience. Turned out it was just the preheating control unit giving trouble, basically just a dodgy cable connection. The mechanic sorted it out pretty quick, only cost me 95 bucks for the repair. Much better outcome than my first time around! The car's running like a dream now, starts up perfectly even in the cold, no more black smoke, and all warning lights are gone. Haven't had a single problem since the fix. Actually kicking myself for not getting it checked sooner. Really hope this helps with your decision. Sometimes these issues sound worse than they actually are. Fingers crossed your repair turns out to be something simple like mine was this time around!

Thanks for the update! I actually went ahead and got it fixed yesterday. You were right, it wasn't as scary as I thought it would be. The mechanic found that two glow plugs were shot and the control module needed replacing. They sorted it all out in about four hours. Bill came to around 350 bucks including parts and labor, not cheap, but definitely better than I expected. The best part? My X7's running perfectly now. No more black smoke, starts up like a charm, and those annoying warning lights are finally gone. Really appreciate everyone's input here, helped me stop putting off the repair. Sometimes you just need that push to get things sorted, right? Guess I learned my lesson about waiting too long when these issues pop up! Thanks again for all the help!