Illumination of the Check Engine Light can be caused by a loose or worn gas cap.Google+
Car Problem Reports
Chevrolet Venture Check Engine Light Due to Gas Cap Issue
Chevrolet Venture Problem
Average Mileage: 97,391 mi (30,000 mi - 163,800 mi)
Visitor, 2005 Chevrolet Venture, 91,000 mi
Check engine light stayed on for a few days, and my wife took vehicle to chevrolet dealer for service. The mechanic said there was a leak around the gas cap area and they fixed. I was charge for 1 hour labor plus tax.
Visitor, 2001 Chevrolet Venture, 30,000 mi
Gas cap was too loose. Tightened it up, problem solved.
Visitor, 2005 Chevrolet Venture, 81,000 mi
Used diagnostic code reader, and it gave me the problem "evaporative system leak". Auto parts store said change the gas cap. Got new cap, problem solved
Visitor, 2004 Chevrolet Venture, 80,000 mi
Loose gas cap = "check engine" light. reset/replaced cap, no problem since.