Problem could be anything. It will need plugging into a diagnostic machine to tell you what the exact problem is. The fault may not be permanent, a fault has been logged into the computer which may have been a "glitch" that lasted for a split second but enough time for the ECU to register it. The only way to safely get rid of the light is to plug in & read then erase the code. Then recheck to see if it comes back, if it does then the fault will need fixing. Diagnostic check circa £35-45. You don't have to use a Ford dealer to get it checked.
MOT Andy
December 2006