To enable cheat mode, activate your PDA and press L2, R2(x2), L2, R2, L2(x2), R2(x3), L2. Press back. Activate the following cheats by entering the corresponding sequences of buttons. You must have the Oct. 23, 2008 online update for these to work:
CHEAT FUNCTION - CHEAT CODE All Airstrikes* - RIGHT, LEFT DOWN, UP, RIGHT, LEFT, DOWN, UP All Costumes* - UP, RIGHT, DOWN, LEFT, UP All SUPplies* - LEFT, RIGHT, RIGHT, LEFT, UP, UP, LEFT, UP All Vehicles* - UP, DOWN, LEFT, RIGHT, RIGHT, LEFT Fill Fuel* - UP, UP, UP, DOWN, DOWN, DOWN Infinite Ammo* - UP, DOWN, LEFT, RIGHT, LEFT, LEFT Invincibility** - UP, DOWN, LEFT, DOWN, RIGHT, RIGHT Nuclear Bunker Busters(25)* - UP, UP, DOWN, DOWN, LEFT, RIGHT, LEFT, RIGHT Unlock Grapping Hook** - UP, LEFT, DOWN, RIGHT, UP
*Activates only for the player that executes it.
**Activates for both players during co-op. Activates for a client who joins a hosts game that has it unlocked.