Illumination of the Check Engine Light can be caused by a loose or worn gas cap.Google+
Car Problem Reports
GMC Safari Check Engine Light Due to Gas Cap Issue
GMC Safari Problem
Ses light came on. code po449 came up on scan tool. replaced purge valve...part shop suggestion..no fix to ses.. swiched out gas cap with another van(astro) ses came on in astro. ran scan on it....same code. replaced gas cap on safari and now no problem!
Visitor, 1998 GMC Safari
Just replaced the gas cap and it went away
i have had problems with the check engine light and gas cap