A monitoring and measuring device for an air supply system of a vehicle, in particular a rail vehicle, includes a compressor which is designed to provide compressed air; a defined volume which is situated downstream of the compressor; a shut-off valve which is situated downstream of the defined volume; a pressure sensor which is provided at any desired position on the pressure line between the compressor and the shut-off valve and is configured to measure the pressure that builds in the defined volume. A first or second air drying device, for example, is used as the defined volume. The pressure curve measured by the pressure sensor can indicate whether there is a fault or a leak. A method for monitoring and for measuring parameters of an air supply system of a vehicle, in particular a rail vehicle is also provided.