Service engine soon light comes on my 2002 Buick Century that only has 54000 miles. What could this mean? Nothing seems wrong with the car. It is oiled regularly.

The service engine light means that the computer has detected that there is something wrong. it doesn't mean that it is anything serious. it could be something very simple. if you want to find out what it is exactly and avoid repair shop costs, take it to auto zone or another parts store. most of them have scanners that they will hook up and tell you why the light is on without charge.