I'm getting an ECM-P008800 (fuel pressure too high) code on my 2010 XC70 T6. VIDA shows the fuel pump duty cycle is at a constant 80% right from the start and doesn't vary no matter the driving situation - idle, slow speed, high speed, etc.. The fuel pressure at start is around 350 kPa and builds to around 650 kPa (reading through VIDA) after a minute or two. It varies between 550 and 650 when driving with the lower pressure when accelerating, which makes sense if the pump duty cycle isn't varying in an on-demand way. I've changed the FPS but with no change. The next steps will probably involve the fuel pump control module (PEM) and/or fuel pump but for each of these the fuel tank must be dropped to gain access. I'm wondering if anyone has any insight into other failure modes that might lead to this type of behavior from the fuel pump. Could there be an issue with the CEM?

From the Design and Function section of VIDA about the PEM:

The fuel pump control module is called the PEM (Pump Electronic Module). The function of the PEM is to supply the fuel pump with voltage and to control the power output of the fuel pump. When the power output of the pump is changed the fuel pressure/fuel flow is also changed.

The fuel pump control module is supplied with battery voltage by the fuel pump (FP) relay and is grounded in the car body. The fuel pump (FP) relay is controlled by the central electronic module (CEM) when requested by the Engine Control Module (ECM).
The engine cannot be started if the power supply to the fuel pump control module is faulty because the fuel pump will not then be powered.

Fuel pump control module is controlled by Engine Control Module (ECM) via serial communication. Then the fuel pump control module controls the fuel pump by adding a pulse-width modulated (PWM) voltage on the fuel pump's ground cable.
This means that the voltage across the pump changes, and then also the fuel pump's output.