Cruise control not working
@jackfrost19 could you provide us a bit more information? How long have you had this problem? How many miles on your '05 Prius?
Check the fuse. You can find the location in the owners ,manual.
Faults w/the engine or transmission can automatically turn off the cruise control. Check the computer’s diagnostic codes.
A problem with the brake light switch could cause this. There is a switch on the brake pedal that causes the brake light to go on. the same switch, is also used to turn off the cruise control. If the switch is bad or a wire is loose it cause the cruise control to not work.