From the main menu, select "Extras", then "Cheats". Enter the code and select the checkmark. A message will appear telling you that a new car part has been unlocked. Go to "Story Mode" and enter the garage to equip your new car part.
|z74hsv -||Unlocks Butterflies (Wheels)|
|36mj5v -||Unlocks Hoistein (Hood Ornament)|
|k4c2sn -||Unlocks Mega Spoiler (Rear Accessory)|