DTC P0451: EVAP Control System Pressure Sensor: Description
WARNING: This page is about a different car, the 2012 Infiniti G25. However, it is still accessible from the selected car via links, so may be relevant.
The EVAP control system pressure sensor detects pressure in the purge line. The sensor output voltage to the ECM increases as pressure increases.
Fig 1: EVAP Control System Pressure Sensor Output Voltage Graph