A Loose or worn gas cap may cause Check Engine Light to illuminate.
Car Problem Reports
Chevrolet 1500 Pickup Check Engine Light Due to Gas Cap Issue
Chevrolet 1500 Pickup Problem
Exhaust & Emissions Affected: Gasoline
Average Mileage: 127,850 mi (67,500 mi - 188,200 mi)
Visitor, 1996 Chevrolet 1500 Pickup, 188,200 mi
Check engine light was on and had a code 420 or 430 can't remember but a new cat. conv. fixed it