A method carries out a brake test on trailer vehicles and/or semitrailer vehicles. The method senses a semitrailer or trailer which has been newly hitched to the towing vehicle, initializes an on-board brake test for the semitrailer brake system or trailer brake system, initiates at least one defined braking process by the semitrailer brake system or trailer brake system after a defined distance has been traveled, and senses and determines the braking effect of the at least one defined braking process as a braking effect actual value which is compared with a braking effect setpoint value which is present. An information signal is output which takes into account the evaluation result.