Method for monitoring at least one system parameter which influences an operating property of vehicles or vehicle trains using an adaptable theoretical model which generates a theoretical vehicle behaviour or vehicle train behaviour from operating data of the vehicle or vehicle train, containing the following steps: a) determination of a real vehicle behaviour or vehicle train behaviour from operating data such as acceleration and / or deceleration of the vehicle or of the vehicle train, b) comparison of the real vehicle behaviour or vehicle train behaviour with the theoretical vehicle behaviour or vehicle train behaviour, and c1) monitoring of the system parameter by the theoretical model if the theoretical vehicle behaviour or vehicle train behaviour corresponds to the real vehicle behaviour or vehicle train behaviour, and c2) if the system parameter exceeds or drops below a predefined limiting value and / or lies outside of a predefined limiting value range, generation of a fault message and / or generation of instructions for the vehicle driver and / or automatic initiation of countermeasures, or c3) adaptation of the theoretical model until the theoretical vehicle behaviour or vehicle train behaviour corresponds to the real vehicle behaviour or vehicle train behaviour and then continuation with step c2), characterised in that c4) monitoring of the system parameter by the adapted theoretical model is carried out according to step c2) only when a deviation between the system parameter acquired with the original theoretical model and the system parameter acquired with the adapted theoretical model does not exceed or does not drop below a predefined limiting value and / or lies within a predefined limiting value range, but c5) generation of a fault message relating to the presence of a fault or of destruction at the vehicle, at the vehicle train and / or in the theoretical model if the deviation between the system parameter acquired with the original theoretical model and the system parameter acquired with the adapted theoretical model exceeds or drops below the predefined limiting value and / or lies outside of the predefined limiting value range. a) determination of a real vehicle behaviour or vehicle train behaviour from operating data such as acceleration and / or deceleration of the vehicle or of the vehicle train, b) comparison of the real vehicle behaviour or vehicle train behaviour with the theoretical vehicle behaviour or vehicle train behaviour, and c1) monitoring of the system parameter by the theoretical model if the theoretical vehicle behaviour or vehicle train behaviour corresponds to the real vehicle behaviour or vehicle train behaviour, and c2) if the system parameter exceeds or drops below a predefined limiting value and / or lies outside of a predefined limiting value range, generation of a fault message and / or generation of instructions for the vehicle driver and / or automatic initiation of countermeasures, or c3) adaptation of the theoretical model until the theoretical vehicle behaviour or vehicle train behaviour corresponds to the real vehicle behaviour or vehicle train behaviour and then continuation with step c2), c4) monitoring of the system parameter by the adapted theoretical model is carried out according to step c2) only when a deviation between the system parameter acquired with the original theoretical model and the system parameter acquired with the adapted theoretical model does not exceed or does not drop below a predefined limiting value and / or lies within a predefined limiting value range, but c5) generation of a fault message relating to the presence of a fault or of destruction at the vehicle, at the vehicle train and / or in the theoretical model if the deviation between the system parameter acquired with the original theoretical model and the system parameter acquired with the adapted theoretical model exceeds or drops below the predefined limiting value and / or lies outside of the predefined limiting value range.