2004 S60R P0193 Fuel Rail Pressure Sensor Circuit High Input

Engine Mechanical problem
2004 All Wheel Drive Automatic 60000 miles
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P0193 Fuel Rail Pressure Sensor Circuit High Input
This is the code we get from the diagnostic reader. I have an S60 R 2004 Volvo. The check engine light comes on and goes off here and there. I am wondering what the code means? And what is causing this?

Thank you,

Brooke