Illumination of the Check Engine Light can be caused by a loose or worn gas cap.Google+
Car Problem Reports
Oldsmobile Alero Check Engine Light Due to Gas Cap Issue
Oldsmobile Alero Problem
Average Mileage: 136,733 mi (122,000 mi - 151,200 mi)
Visitor, 2002 Oldsmobile Alero, 137,000 mi
I had the check engine light come on. My husband took it to an auto shop and the manager asked him if we filled up with gas, which we did. The manager of the shop went out and twisted the gas cap and said that the light would go off soon. The check engine light did go off...now I make sure that I twist the cap several times after filling up with gas. I have not had any problems since then. The best part is that this auto shop did not charge me a penny and knew what the problem was without hooking it up to machines. This auto shop now has all my business, for I know they will not take advantaged of me.
Visitor, 1999 Oldsmobile Alero, 122,000 mi
my check engine light came on saying due to gas cap and it would go away every time i tightened it, but as it turned out this was actually the beginnings of my fuel pump going out and causing low gas pressure.
Visitor, 2000 Oldsmobile Alero, 151,200 mi
service engine soon when I am down to about quarter tank of gas.