In a vehicle, a vehicle system is provided that includes a position determination module for determining the position of the vehicle using an estimation of the error of satellite signals which are received by an earth-based receiver system, and an integrity module for determining an integrity risk for the position data for a vehicle, the risk being derived using time determinations performed by a satellite navigation system. When a threshold value for the integrity risk for the position data is exceeded, the vehicle system generates a warning signal which, by means of modules that are connected to the vehicle system, is designed to prevent the use of the position data for the vehicle. The integrity risk is determined using an estimated value for the error in the received satellite signal, and the receiver system functionally interacts with a plurality of satellites to determine and transmit data to a vehicle system containing a position determination module for determining the position of the vehicle.