10,000,000 Credits (GT Mode Screen):
Select, Left, Right, Right, Down, Up, Up, Left, Down, Up, Right, Left, Down, L1, R1, Select
Pass any license (License Selection Screen):
Select, R1, Select, R1, Select, L2, L2, R2, R2, L1, Select, L1, Select
Gold any specific license test (License Test Selection Screen):
Select, Select, R1, R2, L2, L2, Select, L1, R1, Select, R2, L1, Select
Gold any event (Event Course Selection Screen):
Select, L1, Up, Up, Select, R1, Down, Down, Select, L2, Select, R2, Select
There is an extra code usable in the Mission Hall, which also adds 10,000,000 Credits. It is presumably implemented incorrectly and should instead allow completing any mission. The code is:
Select, R2, Select, R2, L1, L2, L2, Select, L1, R1, Select, R1, Select.