A diagnostic method is provided for a vision sensor of a vehicle. The diagnostic method includes the steps of: determining a first position and a direction of movement of the vehicle; selecting a stationary landmark suitable for being detected by the vision sensor from a landmark database, wherein the landmark is located in front of the vehicle in the direction of movement of the vehicle, wherein a distance from the first position of the vehicle to the landmark is greater than the target range of the vision sensor; detecting the landmark via the vision sensor and, in response to a successful detection of the landmark by the vision sensor; determining a second position of the vehicle; determining an actual range of the vision sensor as the distance between the second position of the vehicle and the landmark.