SES code help P0452

My SES light is on and I just got the code from a scanner. The code is P0452. I just changed the fuel pump and fuel filter two days ago. The indiv. with the scanner tried to erase, but it just re-appeared. What does this mean? Yesterday my 99tahoe was dificult to start but this morning it started up no problem. No hesitating or anything.
Any thoughts???