In a vehicle brake system including first and second brake circuits, a dual-circuit brake actuator, first and second control lines, the first brake circuit including a first brake pressure regulating valve and a first pressure sensor, the second brake circuit including a second brake pressure regulating valve and a second pressure sensor, the brake actuator connected to the first valve via the first control line to control that valve, and, via the second control line, to the second valve to control that valve, a control unit is communicatively connected to the pressure sensors and brake actuator and is adapted to effect a method for detecting a brake system circuit failure including determining a first pressure difference in the first brake circuit and a second pressure difference in the second brake circuit during actuation of the brake actuator, and determining a first comparison value from the first and second pressure differences.