A Loose or worn gas cap may cause Check Engine Light to illuminate.Google+
Car Problem Reports
Cadillac Seville SLS Check Engine Light Due to Gas Cap Issue
Cadillac Seville SLS Problem
Average Mileage: 108,666 mi (68,000 mi - 143,000 mi)
Visitor, 2004 Cadillac Seville SLS, 115,000 mi
Was getting a check gas cap message ans subsequent check engine light, Applied some Vaseline to the oring on the gas cap works for a short time, but a new cap is needed to fix.
Visitor, 2001 Cadillac Seville SLS, 68,000 mi
Check Engine light came on, fuel leak detected, check gas cap came on around a week later, changed and services engine soon turned off.