my son has a 2000 accent. when the car is in overdrive and he is travelling about 65-70 mph the check engine light comes on but if he switches out of O/D the light goes out. Does anyone have any ideas what the problem might be. If he stays under 60 mph in O/D the light wont come on only if he goes above 65 MPH

go to autozone, computer should store the codes.