CheatCodes.com has all the official Underground CD Vol. 1-4 PSX cheats to unlock everything. If you know of any that we don't have, please let us know.
All published and official codes as of Saturday May 18, 2013 for Underground CD Vol. 1-4 are shown below.
At the "Vault" screen of Disc 2, press R2.
At the "Vault" screen of Disc 2, press Circle, Triangle, Circle, Square, Circle.
At the "Vault" screen of Disc 2, hold Triangle + Circle and press Square(2).
At the "Vault" screen of Disc 2, press Triangle, Square, Triangle, Square, Triangle.
At the "Vault" screen of Disc 2, press Square, Triangle, Square, Circle.
At the "Event Center" screen of Disc 1, hold Triangle + Circle and rapidly tap Square.
At the "Bulletin Board" screen of Disc 1, hold Triangle + Circle and rapidly tap Square.
At the "Code Archive" screen of Disc 1, press Square, Circle, Square, Triangle.
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