Toyota PRIUS Owner's Manual page 264

Type 3
Push the "AM", "AM·SAT",
"DISC" or "DISC·AUX" button to turn
on that mode. The selected mode turns
on directly.
Push these buttons if you want to switch
from one mode to another.
If the disc is not set, the compact disc
player does not turn on.
248
26p260
Radio (Type 1)
"FM",
Radio (Type 2)
26p136a
Radio (Type 3)