Pathfinder EGR Valve Issue

Sounds like you're on the right track thinking about the EGR valve. Those symptoms can definitely point that way. The hissing could also be related to a vacuum leak somewhere in the system, which can mess with the EGR's operation. The check engine light is a big clue. Have you tried pulling the error code? That would give you a much clearer idea. It could also be the catalytic converter. Is the smoke black or more bluish? Black smoke often points to fuel issues related to EGR problems, whereas bluish smoke might indicate oil burning.

I haven't pulled the code yet, I'll try to get that done. The smoke is definitely black. If it's the EGR valve, is it something I could try to clean myself, or is it better left to a professional?

Black smoke seals the deal for me, points straight to the EGR valve. Cleaning it might work, but honestly, on a diesel with that many kilometers, it's probably just worn out. Think of it like a sticky door hinge – sometimes you can oil it, but eventually, you just need a new hinge. Messing with the EGR can also cause more problems than it solves if you aren't careful. Given all the symptoms you're experiencing, I'd highly recommend taking it to a workshop. They can diagnose it properly and replace the EGR valve if needed.

Thanks for the advice. I took it to the shop, and you were spot on. It was the EGR valve. They replaced it, and the total cost was 355€. Everything's running smoothly now.