Cheat Codes
Enter the following codes for the corresponding cheat.

Result:
MUS59279 All Muscle Cars
TUN58396 All Drift Cars
M38572343 Micromania Pagani Zonda R
P47203845 Play.com Astom Martin DBR9
G29782655 Gamestation BMW 320si
F93857372 Buchbinder Emotional Engineering BMW 320si
SaveGame
All licenses open, all cars (plus bonus cars), player rank 1st, $72 million cash, all cheat codes unlocked. Extract to your My Documents\Codemasters\GRID folder. Make a backup of your existing savegame folder before overwriting. You may need to edit your profile to reflect the current country in the game.
Trainer
Add 999.999 Drift Points, Kill Race Timer, $100 Million Cash, Unlimited Flashbacks, Disable Other Drivers, Wrecking Ball (Send Other Drivers Flying), Increased/Decreased Acceleration, Increased/Decreased Handling.