Illumination of the Check Engine Light can be caused by a loose or worn gas cap.Google+
Car Problem Reports
Saturn LW300 Check Engine Light Due to Gas Cap Issue
Saturn LW300 Problem
Average Mileage: 158,750 mi (48,000 mi - 271,000 mi)
Visitor, 2002 Saturn LW300, 198,000 mi
Check engine light was on, so I took it to Auto Zone for a code check and they told me I needed a new gas cap. I couldn't believe it, but after getting a new gas cap ($10) the problem went away.
I changed the gas cap and the service light and now the check engine lights are on.
Visitor, 2004 Saturn LW300, 118,000 mi
Engine light on, checked gas cap & it was loose. Tightened it. Light still on. Will try a new cap.
Visitor, 2004 Saturn LW300, 48,000 mi
Check engine light - OBDII stated leak in fuel evap system - new gas cap fixed the problem