are you checking the codes when the car is on? I don't think that it will read the codes if the car is running. at least, that's what mine does. when i get a code while driving, if i check it right then it will say there are none. But when i stop, turn the car off, then turn it "ON" and check the codes they come up. If it's still nothing, have you tried resetting the ECU to make it go away and see if it comes back?