Go to the Scan Menu, Codes Section.

Code	Effect
OPRP3	Unlocks '14 Corvette Stingray.
5CCLL	Unlocks BMW M4.
k3ufh	Unlocks Mig Rig.
TEKGP	Unlocks Nissan 370Z.
rxlwu	Unlocks Pedal Driver.
49txo	Unlocks Porsche 934 Turbo RSR.
t67es	Unlocks Snoopy.