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Here's a close-up view of the vapor pressure sensor:

DriveFast197140918.5556132755

CIRCUIT DESCRIPTION
The vapor pressure sensor and VSV for vapor pressure sensor are used to detect abnormalities in the evaporative emission control system.
The ECM decides whether there is an abnormality in the evaporative emission control system based on the vapor pressure sensor signal.
DTC P0540 is recorded by the ECM when the vapor pressure sensor malfunction.

THe P0450 is a fairly straight forward code on this vehicle. DTC P0540 is recorded by the ECM when the vapor pressure sensor malfunctions. Carefully inspect the vauum line for any cracks, holes or loose/missing connections. Inspect the electrical connector for any loose or broken wires. I fhte visual inspection checks ok, replacing the Vapor Pressure Sensor should solve the problem. It's located under the hood, towards the driver's side rear. (4 cylinder shown in image below).