When a VW radio is disconnected from battery power or installed in a different vehicle, it enters a "SAFE" mode and will not function until the correct code is entered. The code is tied to the radio’s (e.g., VWZ1Z2, VWZ4Z5, or serials starting with 815, 764, 815, 764, 764…).
Once you have your and your VIN (Vehicle Identification Number) , you can use a generator tool or service. Vw Radio Code Generator
Note: This is a simplified illustration; actual algorithms vary. When a VW radio is disconnected from battery