When the firmware boots, when the status of the GPS us unknown, the firmware enables power to the GPS and then listens for data from the GPS module
All GPS modules send data constantly even when they do not have a position fix.
After data is received the firmware knows that a GPS is fitted and operational, and the GPS status changes to "Off", and then turns the power to the GPS off.
If you radio displays "Not fitted" for GPS either its not fitted or its not functional