OBDII code problem

I have a 2001 Pontiac Sunfire that has about 82K miles on it. It is a 4 cylinder with an automatic transmission. Two weeks ago, the check engine light came on and the code was P0440, which is "Evaporative Emission Control System Malfunction". I reset the computer with my Scantool and all was fine. The check engine light stayed off for a week. Yesterday, the check engine light came on again. I pulled the codes and the P0440 code came up again. I do not know what to look for. I did check the gas cap to make sure it was on properly. Can anyone help my diagnose this problem?

Google p0440 lots of info out there.

P0440 relates to the charcoal canister that collects fumes from the fuel system. It can be as simple as a loose gas cap or as complicated as needing to replace the vacuum lines to the canister. Sometimes the vacuum lines come loose or get a hole in them causing this problem. I would check and possibly replace the gas cap. Since the light stayed off for a week that could be the issue. Otherwise dig a little deeper.

P0440 refers to a large leak in your EVAP system, most people equate this code to a loose gas cap.
The control module tests the evaporative emission (EVAP) system for a large leak. The control module monitors the fuel tank pressure (FTP) sensor signal to determine the EVAP system vacuum level. When the conditions for running are met, the control module commands the EVAP canister purge valve OPEN and the EVAP vent valve CLOSED . This allows engine vacuum to enter the EVAP system. At a calibrated time, or vacuum level, the control module commands the EVAP canister purge valve closed, sealing the system, and monitors the FTP sensor input in order to determine the EVAP system vacuum level. If the system is unable to achieve the calibrated vacuum level, or the vacuum level decreases too rapidly, this DTC sets.
Check your evap lines for proper connection