A procedure for diagnosing a tank system of a vehicle with at least two controllable tank ventilation valves, with at least two points of release for a tank ventilation mixture, whereby at least a first point of release runs into an inlet manifold of a combustion engine downstream of a throttle device and at least a second point of release is arranged in an inlet manifold of the combustion engine upstream of the throttle device, especially upstream of a compressor, is thereby characterized, in that for diagnosing the functionality of the tank ventilation system the at least two tank ventilation valves are controlled independently of each other and its functionality can be implied due to the pressure that occurs in the tank system.