Panamera Diesel Woes: Black Smoke and Cold Start Drama

I had very similar issues with my 2018 Porsche Cayenne Diesel last winter. The symptoms matched yours exactly, black smoke, cold start problems, and the constant glow plug light. Took it to the dealer and it turned out the wiring harness between the glow control unit and the digital diesel electronics was damaged. They found several wires were corroded and some connections had worked loose, causing intermittent failures in the glow plug system. This was actually causing cascade failures, affecting the DPF system too. Definitely not something you want to leave unattended as it can lead to more serious engine damage. Had mine fixed at the dealership, the entire harness needed replacement. It wasn't a quick fix, but it resolved all the symptoms completely. I can recommend the certified Porsche center I used. They really know their diesel systems.

Thanks a lot for sharing your experience! It's really helpful to know I'm not alone with these issues. I'm actually leaning towards getting it checked at a dealer after hearing your story. Just curious, do you remember roughly how much the harness replacement set you back? Also, has everything been running smoothly since the repair, or have you noticed any other quirks?

Hey there! Happy to give you an update on my Cayenne's situation. Yes, everything has been running perfectly smooth since I got it fixed, the repair totally sorted out all those annoying symptoms. The glow control unit issue was exactly what they found and fixed, just like I suspected. For the costs, I paid 155€ for the wiring harness repair, which honestly wasn't as bad as I was expecting for a Porsche dealer job. They had to replace the damaged wiring between the glow control unit and the diesel electronics, but it was worth every penny. My cold starts are perfect now, no more black smoke, and that annoying glow plug light finally stays off like it should. I'm actually really glad I went with the dealer on this one. They knew exactly what they were dealing with and got it sorted properly. Been about 6 months now since the fix, and I haven't had a single issue, car runs like a dream! Definitely made the right choice getting it properly fixed rather than letting it drag on. If you do end up getting yours checked, make sure to mention these symptoms, sounds exactly like what I dealt with. Better to get it sorted sooner rather than later!

Just wanted to update everyone, I took my Panamera to the dealer yesterday following your advice, and you were spot on! Had almost the exact same issue with the wiring harness. The diagnostic showed multiple connection problems, and they found some corroded wires too. The repair cost me a bit more than yours, came to about 190€, but honestly, I'm just relieved it's fixed. Picked up the car this morning and what a difference! No more black smoke, starts up perfectly even in the cold, and that annoying glow plug light is finally gone. The idle is smooth as butter now. Really appreciate everyone's input, especially about going to the dealer. Was a bit nervous about the potential costs, but it was totally worth it to have it done right. They even gave the car a quick inspection and confirmed everything else is running great. Thanks again for helping me make the right call on this one. Time to enjoy some proper Porsche performance again!