2001 pontiac grand prix gt PO446 code how do i fix it? what else do i change?

Tests/Procedures: 1. Install a scan tool and look for the fuel tank pressure sensor voltage reading. 2. With the key off, remove the gas cap then turn the key on and check voltage. It should be 1.3-1.7 volts. 3. If not in that range, check the wires to the sensor and make sure it has a good 5 volt reference on the Gray wire and ground on the Black. 4. Check the Dark Green wire back to the Powertrain Control Module (PCM) for opens or shorts. 5. Check the vent solenoid for plugged up. Remove the hose going to it and see if can blow through the solenoid easily. Tech Tips: If this sensor is off from the beginning, when it runs the test it will not see the change it is looking for, even though the rest of the system is functioning correctly. It may not set a code for that sensor out of range unless it goes to an extreme value.