The fuel pressure limiting valve is located on the top of the fuel railFuel pressure at the fuel rail is monitored by the fuel rail pressure sensor. If fuel pressure becomes excessive, the pressure limiting valve opens and vents excess pressure into the fuel drain circuit.
Hi, and welcome to Just Answer!
To answer your question, the ECM uses the fuel control actuator to control the fuel pressure in the common rail (high side) of the system.
From the service information;
"The Fuel Control Actuator (FCA) is an electronically controlled solenoid valve. The ECM controls the amount of fuel that enters the high-pressure pumping chambers by opening and closing the FCA based on a demanded fuel pressure."
You are correct, it's not the same as the fuel pressure limiting valve.. That's on top of the rail, and is essentially a high pressure relief valve.. Should the FCA (or the fuel pressure sensor) fail and pressure in the rail get to high, the limiting valve opens and dumps pressure back to the return side of the system to prevent damage.
I hope this helps you out, any questions don't hesitate to reply back and ask!