voltage which lies between normal voltage and a lower limit value undervoltage or a fault in the return flow pump or a fault in an outlet valve of a rear wheel brake in step 118 the previously mentioned steps 102 through 106 to determine the vehicle speed vehicle deceleration a braking action and actual value u03b4v are first performed if step 104 has indicated that no braking action is present in step 120 the actuators of the rear wheels are set so that a pressure reduction is initiated during a braking action in the event one of the faults outlined above is present in step 122 the difference between setpoint and actual value is obtained and if a tolerance value u03b4not2 is exceeded then in step 124 the inlet valves of the rear wheels are closed set iv if the difference between setpoint and actual value is greater than tolerance value u03b4not2 step 126 then the rear wheels are slower than the front wheels so that in step 128 the inlet value can be opened to reduce the pressure reset iv if the difference is within tolerance range u03b4not2 then in step 130 similarly to step 114 the rear wheel braking pressure is built up in the context of a pulse series the outlet valves and return flow pump are not actuated if one of the aforementioned faults is present if step 100 detects that a rotation speed sensor is faulty then in step 132 the faulty wheel signal vradf is replaced by wheel speed signal vrad of the same side steps 102.