Pause the game and enter the codes at the Map Screen. 

Respawn power-ups:
     Press Y, A, A, Y, X, B, B, X, A, X, B, Y.

All vehicles:
     Press Up, Down, Up, Down, Y, A, Y, A, X, B, B, X.

Infinite Ammo:
     Press Y, X, X, B, Y, X, X, B.

More money:
     Press Y, B, Y, B, X, A, X, A, Down, Up.

Restore health:
     Press X, B, X, B, X, B, X, B.

Tornado:
     Press Y, B, A, X, X, A, B, Y.

Decrease RIOT level:
     Press Y, B, A, X, Y, B, A, X, Down.

Increase RIOT level:
     Press Y, B, A, X, Y, B, A, X, Up.