Diagnostic method for a braking system

A diagnostic method for determining the leak-tightness of at least one seal function, at least one valve function, or both, in a braking system with at least two brake circuits, wherein each brake circuit has a brake circuit hydraulic line to which, in each case, at least one wheel brake is connected, wherein the braking system has a regulatable pressure source which serves at least to effect a pressure build-up in the wheel brakes and at least one pressure sensor which determines the pressure in a brake circuit, wherein a control unit controls the valves and the regulatable pressure source, the method comprising:

• performing, by the control unit, at least one braking diagnostic procedure, the at least one braking diagnostic procedure comprising using one or more pressure measurements, using sensing of brake actuation device travel, or using both, wherein the at least one braking diagnostic procedure is performed following completion of a braking action:
• either at a pressure which is still present at the completion of the braking action in, or which is input into, the braking system, in one or both brake circuits and/or a hydraulic line or a working chamber of a piston-cylinder system, or at a lower pressure;
• or at a pressure of at most 30 bar, wherein the pressure is in, or input into, the braking system, in one or both brake circuits and/or a hydraulic line or a working chamber of the piston-cylinder system;
• wherein during the performing the at least one brake diagnostic procedure, the regulatable pressure source does not cause any change in pressure in one or both of the brake circuits.