I'm assuming that the light is yellow with a picture of an engine block. It usually means that there is an electrical sensor faulty somewhere. However, it could just be some moisture which is causing a bad contact. By the book you should take it to a mechanic who has a scanner which will tell you where the fault is. From experience i would keep using the car for about 20 miles (again assuming that it is still running fine) and hopefully any moisture will evaporate which would then cause the light will extinguish.