2014 Prius C, has happened before but I forgot the solution. How to make the speedometer display use miles per hour instead of kilometers. My miles per gallon etc are all OK, but it shows I am going 60 K/hr instead of 36MPH!
Press the "trip" button on the steering wheel until the information display shows the total miles accumulated since new (i.e., NOT the "Trip A" or "Trip B" displays). Press and hold the "trip" button on the steering wheel until the speedometer units change.