my engine light has come on 3 times in past 2 months on 2001 Lexus IS300

the engine light comes on, but the car feels fine. I've radjusted the gas cap. It turns off after a couple of days. My headlight leveling light has come off and on as well. I took it to my mechanic but they can't check it unless the light is on. He says it's nothing if the light goes off and only to worry if it flashes?? Not sure what is happening here.

Asked by for the 2001 Lexus IS300
I think scan test will show codes. Have this done and post codes so we can help.