When a brake of a tractor is released, a control unit having a computer built therein monitors the pressure of working fluid output from a trailer control valve that controls a brake of the trailer in conjunction with the brake of the tractor. When time required for a pressure of the working fluid to decrease to a predetermined pressure is a predetermined time or longer, the control unit determines that the trailer is coupled with the tractor. When the time is less than the predetermined time, the control unit determines that the trailer is not coupled with the tractor.

An apparatus associated with an assistance system of a vehicle includes a device configured to control an adaptive leveling process of the vehicle. The device receives first position data topography data and first leveling process data. The device determines second leveling process data associated with the second position data as a function of the topography data and/or the first leveling process data. The device is also configured to output an electrical control signal as a function of the second leveling process data for the leveling process of the vehicle during the second journey.

Methods and systems are provided for a vehicle towing a trailer. In one embodiment, a method includes: receiving, by a processor, sensor data from one or more sensors of the vehicle; estimating, by a processor, a steering torque value based on the sensor data; estimating, by the processor, a steering angle value based on the sensor data; determining, by the processor, a trailer tongue value based on the steering torque value and the steering angle value; and generating, by the processor, a control signal to control the vehicle based on the trailer tongue value.