The is not magic—it is a mathematical necessity. Whether your radio is locked after a battery change or you are programming a new key, the 17-character VIN on your dashboard is the master key to retrieving that elusive 4-digit number.
If your car has had its engine or computer modules changed, the code linked to your VIN in the database might no longer match your car. In these cases, a specialist can read the code directly from the vehicle's hardware: VIN Lookup – VIN Decoder on CARFAX vauxhall security code from vin link
How to find your car radio code and unlock your stereo - RAC The is not magic—it is a mathematical necessity