Twisted Metal 4

Activate memory card:
Enter Start, Start, Start, Start, Start as a password.
Select any desired game settings and begin a game.
A prompt to save will appear after exiting the option menu.

Unlimited special weapons:
Enter Triangle, L1, Down, Triangle, Up as a password.

CPU only shoots at player 1:
Enter Right, Triangle, Right, Triangle, L1 as a password.

All weapon pick-ups are napalms:
Enter Right, Left, R1, Right, Circle as a password.

All weapon pickups are Remote Bombs:
Enter Up, Right, Down, L1, Triangle as a password at the options menu.

No heath in deathmatch mode:
Enter Triangle, Down, Triangle, Circle, Triangle as a password at the options menu.

No heath in tournament and deathmatch modes:
Enter Down, R1, Down, Start, Circle as a password at the options menu.
(Information from Cheat Machine)