Peugeot 4008 crankcase ventilation issue

Interesting. I had similar symptoms with my old Volvo: check engine light, loss of power, and even some smoke. Was yours also diagnosed as a crankcase ventilation problem? How many kilometers has your car done? If the crankcase ventilation is defective, it can cause a leak, which would explain the smoke and loss of power. Did you check for any obvious leaks around the engine?

My 4008 has 224776 km on it. I haven't spotted any obvious leaks myself. Is there anything specific I should be looking for, or is it best to just take it to a workshop?

With that mileage, a crankcase ventilation issue is certainly plausible. While you might not see an obvious external leak, the defective valve can cause internal pressure issues, leading to the symptoms you described. Given your expertise level, I'd recommend a workshop visit. They can properly diagnose the crankcase ventilation system and confirm if that's the problem.

I took it to the workshop, and you were spot on – crankcase ventilation valve was indeed defective. Repair cost me 360€, but the car's running much better now!