Agricultural tractor

The vehicle has a hydraulic brake system, and a pneumatic brake system for a trailer coupled with the vehicle. A pneumatic coupling head (1) transfers pressurized air between the vehicle and the trailer. A valve (13) is integrated into the coupling head and inserted between a coupling head line (5) and a branch line (7). The valve is automatically transferred to an opening position during coupling of a counter-coupling head with the vehicle, where the coupling head line is pneumatically connected with the branch line in the opening position. A sensor detects pressure in the branch line. The sensor is designed as a path sensor or pressure sensor.