If you power off the bike and jumper the green service connector, then power on the bike, the FI indicator with cycle through the stored fault codes.
Note that these are stored fault codes which may not be current unless you cleared the previous stored fault codes.
It will blink to indicate the fault code number.
Fault codes can be two digits as well, so the FI indicator will have a slightly longer blink to indicate the left digit (tens digit) then the shorted blink for the right digit (single digits).
The service manual doesn't elaborate on the operation of individual components.
For the fuel pressure regulator, a frequent side effect of a failing unit is excessive fuel being injected into the engine. Up to the point where it fouls the plus and collects in the exhaust and drips to the ground.
The RC51 used 50 PSI fuel line pressure.