P0443 code ???

[stevenjtaylor]

I have a 2008 Grand Prix base model that keeps throwing a P0443 code (see attachment). I've tried different gas caps, replaced the purge valve, looked at fuses and have had no luck. I can clear the codes and the check engine light, but they come right back immediately after I turn the car off and then restart it. I have not noticed a vacuum sound when I remove the gas cap. I would really appreciate any advice on this. Maybe an electrical issue since it pops up immediately at ignition???