ENGINE LIGHT ON: P0453 evaporation emission control system pressure sensor high input

2005 Toyota Prius

got the engine light on and checked it with the OBD II got the following:

p0453 : evaporation emission control system pressure sensor high input

what is my next move.. dealer or regular mechanic? try to save a student some loan money...



History: got the car as is and the dealer gave me this sensor ( like a bent black plastic) and said he took that off from the top of the gas tank to test it on another car to see if it works and he claimed that the sensor worked and once installed it should take car eof my problem so I gave it to my body shop guy and he said he did put it in on top of the gas tank. i went home and reset the engine light and was happy for 3 miles till the light came back with the same error.

possibilities:
1. the sensor was not good
2. the body shop didnt know how to install it
3. the problem is not the sensor at all
4. there is another part involved plus the sensor

so please help me out here.. and please keep me away from the dealers unless i really have too.