The article considers the possibility of identification by automatic control systems of the braking mode of a vehicle combination with a partially filled tank. The algorithms of operation of modern vehicle stabilization systems are based on a reaction to approaching critical points of loss of stability, while the forces with which a fluid acts in a partially filled tank on a vehicle sometimes have a rapid rise when the speed or direction changes, which leads to a decrease in the efficiency of such systems. Automatic identification of the braking mode with a partially filled tank can make it possible to predict the negative consequences of fluid flow and carry out preventive manipulations to stabilize the vehicle until it actually approaches critical points of loss of stability. To solve the problem, a comparative analysis of changes in the magnitude of the normal reaction of the supporting surface on the axis of the vehicle combination during braking with a partially filled tank semi-trailer and an equivalent rigidly fixed load was carried out. Such an analysis showed that in the case of transportation of rigid cargo, the load on the axles of the vehicle combination varies linearly and in proportion to deceleration. In the case of a partially filled tank, the axle load varies non-linearly due to the trigonometric nature of the fluid movement relative to the tank. This feature allows you to distinguish between these modes. As a result, it was proposed to use an identifier that can detect the braking mode of a vehicle combination with a partially filled tank by determining the nature of the changes in axle loads. To calculate the identifier, the axle loads and vehicle acceleration over time are used, and data on the design features of the vehicle combination are not required. Keywords: vehicle combination, tank vehicle, partially filled tank, stability, braking.