Peugeot 807 Incorrect Fuel Composition Error

I had a similar issue with my 807. Same symptoms, engine light and stalling. The error pointed towards a bad fuel mixture. Have you checked the combustion chamber for any unusual deposits? Perhaps the fuel itself is contaminated.

Combustion chamber? Contaminated fuel? How exactly did you check all of that?

In my case, the mechanic noticed some unusual engine knock. After examination, it turned out to be a defective plug connection. I would recommend going to a trusted workshop. I was lucky and this has cost me only around 95€.

Thanks for the tip, defective connector was exactly the problem. Replacing it solved the issue as you suggested.