The invention relates to system for the monitoring of the air pressure in a motor vehicle tyre, by means of a sensor (14), arranged in the air volume of an air spring (10). Noise vibrations are generated in the air volume as a result of the vibrations of the wheel (2), which are picked up by the sensor (14). The characteristic frequency of the wheel (2) is determined by an evaluator circuit (18) and compared with the characteristic frequency of said wheel (2) with a given preset air pressure. Should the determined characteristic frequency differ from the characteristic frequency with a given preset air pressure by more than a predetermined amount, then the evaluator circuit (18) generates an error signal. The sensor is in the form of a microphone or pressure sensor.
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