Pause the game and press L2, R2, R2, L2, R1, L2, L1, Left, Right, L2, Down, R2. Repeat this code to disable it.
Increase Speed:
Pause the game and press R1, L1, L2, R2, Right, Right, Right. You can go even faster by entering the code again.
Weightless:
Pause the game and press L1, R2, R2, L2, R2, R2. This code only works for player one, even in multiplayer.
Matrix Mode:
Pause the game and press R2, L2, L1, R1, Left, Left, Left. Use this code to slow everything down.
Invisibility:
Pause the game and press R1, L1, L1, R2, L1, L1, L2.
What You Unlock By Beating Missions:
Beat the missions listed to get the corresponding prize:
Super Buggy: Available at beginning of the game
Super Buggy Boost: Mission 3
D-5 Hondo: Training Mission 3
D-5 Hondo Oil Slick: Mission 8
Baja Truck: Mission 4
Baja Truck Bombs: Mission 7
ATV Monster: Mission 10
ATV Monster's Speed Burst: Mission 14
Du Monde: Mission 13
Du Monde Oil Slick: Mission 21
Sahara Special: Mission 17
Sahara Smoke Screen: Mission 18
Grenadier: Mission 24
Grenadier Bombs: Mission 25
Kavostov Halftrack: Mission 27
Kavostov Halftrack's Smoke Screen: Mission 29
Vietnam Map: Mission 9
Georgian Russia Winter Map: Mission 22