service engine light

[importmd]

my light has been come on for the past week. it seems to stay on for a few days then go away.

its throwing two codes:
P0452 Evap emission control system pressure sensor LOW
P0453 Evap emission control system pressure sensor HIGH

what could this be? thanks

and yes my gas cap is tight.

 

[Sepiroth]

Are you sure the fuel cap is sealing proerly? That would set the code too

Do you fill up the truck while it is running?

It might be the fuel tank pressure sensor that has gone bad. The thing that sucks is you have to drop the tank.

 

[importmd]

i dont know if my cap is good or not, in the winter i always leave it running while filling it, but the light came on days after filling it, ive never had this problem before. i dont understand how it can throw codes for high/low pressure? shouldnt it be one or the other?