Pinhole rust on steel fuel-filler necks in the salt belt can cause this. Hoses too like Coby says. Don't know what part of the country you're in so not sure if it could be salt-induced.
An ever-so-slightly loose gas cap can also cause the condition. A new gas cap with a fresh seal is a possible cheap solution. I had a saturn L that also regularly caused this, usually it's fixed by tightening the gas cap. This error is extremely sensitive to even the slightest leaks. Maybe there's a dirty ground?
Last edited by gbreadman; 05-21-2016 at 07:26 PM.