Illumination of the Check Engine Light can be caused by a loose or worn gas cap.Google+
Car Problem Reports
Buick Park Avenue Check Engine Light Due to Gas Cap Issue
Buick Park Avenue Problem
Average Mileage: 115,000 mi (60,000 mi - 175,000 mi)
Visitor, 2001 Buick Park Avenue, 175,000 mi
Car drove fine, but Service Engine light was on. Had it checked out and was told of a small air leak and gas caps loose their seal after a while. Got a new gas cap and the light went out.
Visitor, 2003 Buick Park Avenue, 60,000 mi
Fuel cap will not stay on.
Visitor, 2000 Buick Park Avenue, 100,000 mi
it's not fixed