PROBLEM RESOLUTION:

On a hunch, I tested the theory that, when stopping to refuel, the engine must BE RUNNING when you press the "fuel pump" button. If the engine is off, and only "ignition ON", the gas flap springs open, but the EVAP Vent is NOT held open at engine shutdown. This frustrates refueling.


This defect theory was tested and verified. The problem with refueling is:

1. The EVAP Vent Valve must be open when fueling, to expel tank air as fuel displaces it.
2. Traditionally, in EVAP system design, the Vent Valve is normally OPEN when the car is off/parked, meaning the car doesn't need to decide when you are parking vs. getting out to refuel.
3. In this 2013 XC70 (T6 US California emissions model), the EVAP Vent Valve is closed when the car is off & parked, to prevent slow emission of gas fumes through the vent air-filter. The car cannot be refueled in this mode.
4. The software decides you're stopping to refuel based on pressing the "fuel pump" button while the engine is still running, and leaves the Vent Valve OPEN at engine shutdown.
5. If you forget to punch the "fuel pump" button before cutting off the engine, but instead come back in and press it with "ignition ON" but no engine running, the valve remains CLOSED and pumping gas is frustrated.

This might have been better handled in the software design by echoing the "fuel pump" button-press with a console message "Ready to refuel". This message would be only be shown if the Vent Valve were open and the tank ready to receive.