It depends. If you get a brand new unit which was never connected to another car, it will learned the VIN during the first connection and never ask you for a code. If you test a brand new unit with just 12V+ and gnd, it will start prompting you for the code after a couple of cycles. Then, when you install it, it will learn the VIN and never prompt you again unless it sees another car. Once it knows a VIN it will allways prompt you for the code if it gets connected to another car or just power.