Conduite de retour de carburant obstruée

The line that carries unburnt fuel from the rail back to the tank, and the part most often forgotten when rail pressure reads high. On a returning system the pump delivers far more fuel than the engine uses; the regulator bleeds off the surplus and the return line takes it away. Restrict that path and the surplus has nowhere to go, so rail pressure climbs even though the pump and the regulator are both working exactly as designed.

It also explains a symptom that otherwise looks unrelated — hot fuel. Fuel that cannot leave the rail is recirculated past a hot engine again and again instead of being replaced with cool fuel from the tank, so the fuel temperature reading rises steadily under sustained load. A rail pressure complaint and a fuel temperature complaint stored together point here rather than at either sensor, which is why this cause sits on both.

What blocks it is usually not debris. A crushed or kinked line after work in the area, a collapsed flexible section that has softened with age, or an in-line filter or check valve fitted the wrong way round will all do it. Check the line's routing and squeeze the flexible sections before condemning the regulator — the regulator is the expensive part and the line is the one that was disturbed.