I've got a 2005 Hyundai Accent (automatic) that in the last 5 days has had its engine light turn on after a hard shift and getting stuck in 4th gear. The trans was inspected externally and not issues found. The a couple days later the engine light came back on after a slip in a lower gear (between 35-45 miles per hour). Again had the error coeds checked, external trans inspection turned out to find nothing. Engine light then came on after same symptom. I parked the car over night and this morning the check engine light is off and the car is shifting properly. What might be the problem? Bad gear box? Pulse generator? Have any ideas of the costs involved to fix it?