One problem related to transmission sensor has been reported for the 2012 Ford Fiesta. The most recently reported issues are listed below. Please also check out the statistics and reliability analysis of the 2012 Ford Fiesta based on all problems reported for the 2012 Fiesta.
I bought a 2012 Ford Fiesta and had the transmission sensor replaced under factory warranty. Did not drive the car 5000 miles and the trans sensor messed up again causing the transmission to not shift out of first and second gear without hesitation and vibrations. Shifts fine from second on! per the dealer they stated this is a huge issue with Fiestas and focuses from 2010 and up!.