Black Smoke & Glow Plug Woes: Infiniti M Diesel Help

I had similar issues with my 2015 Infiniti Q50 Diesel last winter. The symptoms were almost identical to yours black smoke, slow starts, and glow plug light staying on. Turned out the wiring harness between the glow control unit and ECU was damaged, causing communication issues. Got it fixed at the dealer since it needed specialized diagnostic equipment. They had to replace the entire wiring harness and reprogram the ECU. It wasn't a quick fix took them two days to complete the work. It was quite serious as the faulty wiring was causing the glow plugs to malfunction and the engine to run rich (hence the black smoke). Based on your symptoms, I'd strongly recommend getting it checked at a certified Infiniti dealer. Regular mechanics often miss these specific electrical issues in diesel engines.

Hey, thanks for sharing your experience! That's really helpful to know about the wiring harness being the culprit. Sounds exactly like what I'm dealing with. Do you remember roughly how much you ended up paying for the whole repair? And has everything been running smoothly since then, or have you had any other issues pop up?

Hey again! Yeah, I can actually tell you exactly what I paid it was 395 Euro for fixing that wiring harness issue. Let me tell you, ever since they sorted out that glow plug malfunction, my Q50's been running like a dream! It's such a relief not seeing that pesky glow plug light anymore, and the black smoke issue is completely gone. The best part? Cold starts are super smooth now, just like when the car was new. I can tell you getting it fixed at the dealer was definitely the right call they knew exactly what they were dealing with. Haven't had a single problem since then, and it's been over a year now. Trust me, once you get that wiring sorted between the glow control unit and engine control unit, you'll notice the difference straight away. The car just feels so much more responsive. Worth every penny if you ask me!

Thanks so much for all the details! I took your advice and finally went to the Infiniti dealer yesterday. You were spot on it was exactly the same wiring harness issue! The mechanic showed me where the damage was, and honestly, it looked pretty bad. Cost me a bit more than yours though 450 Euro, but they also did a full diagnostic check while they were at it. Just picked up the car this morning and wow, what a difference! No more black smoke, starts up like a charm, and that annoying glow plug light is finally off. Should've done this weeks ago instead of worrying about it. Really appreciate you sharing your experience saved me from going to another unusual mechanic who might've just made things worse. The dealer even gave me some tips about preventive maintenance to avoid similar issues in the future. Guess sometimes paying a bit extra for dealer service is worth it, especially with these complex diesel systems. Thanks again for pointing me in the right direction!