1992 Olds Cutlass Supreme Coup International Series Hurst 3.4L DOHS

The Service Engine Soon warning light comes on sporatically. It seems to come on when I have been driving at highway speed and the change to driving 45 -25 mph but this is not always. I have the car serviced regularly. The light has never come back on after a restart when it has been on. Because of this I have not been able to have it checked for codes. Any ideas? The car’s actual mileage: 196,687