2004 Impala p0452
 

I have been asked by a friend of mine to work on his 2004 impala when I check the codes it's showing the p0452 code. here is the funny thing I can clear it & recheck the codes (before turning key or doing ANYTHING ) it STILL shows the SAME CODE!! I've changed both Solenoids (Purge & the vent) the fuel pump has been changed out with a new one (so it's got a new FTP sensor as well) not sure if it had this code before the fuel pump was changed or not ?? so PLEASE help it's about to drive me to drinking ( like I need a reason for that ha ha :D)
anyways thanks in advance