Re: 2006 F150 Engine Failsafe Mode
Get the vehicle scanned for codes. Generally fail safe can either be transmission or cooling (the two major ones, anyway). As you mentioned the vehicle drove fine chances are the PCM detected something wrong and its stored in the memory. The code will disappear after you start the vehicle 50 or so times, so get it checked out in a couple days to make sure there really isn't a possible problem that may get you stranded.
'00 Durango R/T 360ci 290hp (modded); 138,500m
'06 Pontiac G6 GT 3.5L 220hp; 44,000m
'12 Chrysler 200 Limited 3.6L 283hp; 13,000m
'99 Taurus 3.0L 2V Vulcan 145hp; 154,300m - Traded
Amsoil in all vehicles!