2006 Saturn Ion

just got my new saturn.. this morning on a 30 degress i started the engine and was rushing to go to work and did not warm up the car! i turned on the heater immediately and after a few minutes the engine light light up... drove it for almost 25 minutes and did not give me any problems at all.. the heater was working fine.... but the light stayed on.. when i got to the parking lot.. i turned off and waited a few minutes... i started the engine on and the engine light came on again... i have tried 3 times since 4hrs has passed and the ligth still on... open the hood and no sign of anything.. oil ok and water ok... how can i make the light go off.. maybe a fuse?? please advise!!

thanks
mando