Choose "Options" from the main menu, then select "Game Status," press O to call up the passcode menu, then enter any of the following cheat codes:
WMNNWLHTSCUCLH-Unlock all secret characters and levels
MONSTER_WHEELS-Wheels are double size
SAME_CHARACTER-In two-player mode, both characters can use the same vehicle
REDUCE_GRAVITY-Less gravity
GO_SIGHTSEEING-No enimies in Arcade mode
I_WILL_NOT_DIE-Invincibility
HARDEST_OF_ALL-More difficult enimies
DEADLY_MISSLE-Enimies start with secondary weapons