Just click the pic below and sign in with your Coke Rewards account, providing you already have one, or make one. You will receive an email with the code, that is to be redeemed in the Redeem Code section of the game. Yes, this is old, but it still works. I just tested it out. The code also works on any system 
Start Need for Speed: Shift with one of the baddest cars already unlocked - the exclusive Coke Zero Dodge Viper SRT10.
Start Need for Speed: Shift with one of the baddest cars already unlocked - the exclusive Coke Zero Dodge Viper SRT10.