To do a burnout at any point on a track hold R2 + L2 and press Circle and then release Circle to perform a burnout. This does not work with some vehicles, the best vehicle to do it with is the Rally Car. The best terrain is in the mud.
This feature is unlocked during gameplay by pausing the game and holding L1 + L2 + L3 + R1 + R2 + R3 + Left analog-stick Right + Right analog-stick Left. You will hear a confirmation sound if you have entered the code correctly.
The following codes are entered by holding down all the indicated buttons and pushing the analog sticks in the direction which is required. If the code has been entered correctly you will hear a noise as confirmation.
Unlock Everything: At the Main menu hold L1 + L2 + R1 + R2 + R3 (Analog sticks pushed Up) +L3 (Analog sticks pushed Down).
Unlock Big Head (ATVs and Bikes): During gameplay pause the game and hold L1 + L2 + R1 + R2 + R3 (Analog sticks pushed Right) + L3 (Analog sticks pushed Left).