Peugeot Malito!

But not the ECU; in that case it would be the BCI. The ECU doesn't control those things; it only processes information from the sensors, nothing more. And how are the engine grounds? Try putting a new one on, from the battery's negative terminal to the engine

Hi:
Your problem might be smaller than it seems. Have you tried changing the fuel tank cap? Modern vehicles come equipped with plastic tanks, which need to "breathe" because they expand and contract due to being made of plastic and the weight of the fuel. If the cap is airtight, not enough air will get in for the tank to inflate, and the gauge will read full when it's not.
It's like drinking from a bottle without leaving room for air to enter as the liquid comes out... Does that make sense?
Good luck!

Greetings from Córdoba, Argentina.

I'm wondering if it could be that you have air in the tank and the fuel gauge is giving you a bad reading?
To check that, when you're driving and the car stalls, you have to get out and open your fuel tank. If you hear the tank deflating, it's because you had an air problem.

I think your problem is with the fuel level sensor; you should replace it. But keep in mind that these sensors require an initial learning process. If you install a new one and don't follow the steps, it won't work. Tell your mechanic to check with the dealership. Best of luck!