Original URL: http://www.psxextreme.com/psp-cheat-print/5.html
Twisted Metal: Head On
Cheats
Enter while playing Story or Challenge mode. Won't work in link or online games.
Invincible: Right, Left, Down, Up, L+R
Infinite Ammo: Triangle, Triangle, Down, Down
4X Damage: X, Triangle, X, Triangle

Unlock Secret Characters
Dark Tooth: Complete Story Mode
ATV: Complete L.A. Stage in Story Mode
Cousin Eddy: Complete L.A. Stage in Story Mode
Mr. Slam: Complete L.A. Stage Sub-Level
Axel: Complete Russia Stage Sub-Level
Crimson Fury: Complete Monaco Stage Sub-Level
Hammerhead: Complete Tokyo Rooftop Stage Sub-Level

Unlock Deathmatch Levels
Egypt: Complete Egypt Stage Sub-Level
Greece: Complete Greece Stage Sub-Level
Paris: Complete Paris Stage Sub-Level
Rome: Complete Rome Stage Sub-Level
Tokyo Streets: Complete Tokyo Streets Stage Sub-Level