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: 150,000 mi (125,000 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.