Method for diagnosing supply-air-side pressure fluctuations and/or output-side leaks in a regulated double-cone air power amplifier (100; 200; 500), 1.1 the double-cone air power amplifier (100; 200; 500) being regulated by a closed-loop controller with a setpoint value and an actual value of a regulated variable; the method comprising the following steps: 1.2 initial measurement of at least one downward step, the measurement of a downward step comprising the following: 1.2.1 waiting for a downward step of the setpoint of the regulated variable; 1.2.2 ensuring an exclusively proportional closed-loop controller; 1.2.3 recording the time characteristic of the actual value of the regulated variable, 1.2.3.1 starting with the downward step of the setpoint and 1.2.3.2 ending when no further change in the actual value is detected within a specified measuring accuracy; 1.2.3.3 whereby a curve with two inflection points is obtained; 1.2.4 determining a reversal amplitude and/or a reversal duration, 1.2.4.1 wherein the reversal amplitude is the difference between the actual values of the curve at the two inflection points; 1.2.4.2 wherein the reversal period is the time interval between the two inflection points; 1.3 re-measuring a downward step; 1.4 diagnosing a supply-air-side pressure drop if the reversal amplitude of the re-measuring is smaller than the reversal amplitude of the initial measuring by more than a specified tolerance; and/or 1.5 diagnosing an increase in supply-air-side pressure if the reversal amplitude of the re-measurement is greater than the reversal amplitude of the initial measurement by more than a predetermined tolerance; and/or 1.6 diagnosing increased leakage on the output side if the reversal duration of the re-measurement is shorter than the reversal duration of the initial measurement by more than a predetermined tolerance. 1.1 the double-cone air power amplifier (100; 200; 500) being regulated by a closed-loop controller with a setpoint value and an actual value of a regulated variable; the method comprising the following steps: 1.2 initial measurement of at least one downward step, the measurement of a downward step comprising the following: 1.2.1 waiting for a downward step of the setpoint of the regulated variable; 1.2.2 ensuring an exclusively proportional closed-loop controller; 1.2.3 recording the time characteristic of the actual value of the regulated variable, 1.2.3.1 starting with the downward step of the setpoint and 1.2.3.2 ending when no further change in the actual value is detected within a specified measuring accuracy; 1.2.3.3 whereby a curve with two inflection points is obtained; 1.2.4 determining a reversal amplitude and/or a reversal duration, 1.2.4.1 wherein the reversal amplitude is the difference between the actual values of the curve at the two inflection points; 1.2.4.2 wherein the reversal period is the time interval between the two inflection points; 1.3 re-measuring a downward step; 1.4 diagnosing a supply-air-side pressure drop if the reversal amplitude of the re-measuring is smaller than the reversal amplitude of the initial measuring by more than a specified tolerance; and/or 1.5 diagnosing an increase in supply-air-side pressure if the reversal amplitude of the re-measurement is greater than the reversal amplitude of the initial measurement by more than a predetermined tolerance; and/or 1.6 diagnosing increased leakage on the output side if the reversal duration of the re-measurement is shorter than the reversal duration of the initial measurement by more than a predetermined tolerance. 1.2.1 waiting for a downward step of the setpoint of the regulated variable; 1.2.2 ensuring an exclusively proportional closed-loop controller; 1.2.3 recording the time characteristic of the actual value of the regulated variable, 1.2.3.1 starting with the downward step of the setpoint and 1.2.3.2 ending when no further change in the actual value is detected within a specified measuring accuracy; 1.2.3.3 whereby a curve with two inflection points is obtained; 1.2.4 determining a reversal amplitude and/or a reversal duration, 1.2.4.1 wherein the reversal amplitude is the difference between the actual values of the curve at the two inflection points; 1.2.4.2 wherein the reversal period is the time interval between the two inflection points; 1.3 re-measuring a downward step; 1.4 diagnosing a supply-air-side pressure drop if the reversal amplitude of the re-measuring is smaller than the reversal amplitude of the initial measuring by more than a specified tolerance; and/or 1.5 diagnosing an increase in supply-air-side pressure if the reversal amplitude of the re-measurement is greater than the reversal amplitude of the initial measurement by more than a predetermined tolerance; and/or 1.6 diagnosing increased leakage on the output side if the reversal duration of the re-measurement is shorter than the reversal duration of the initial measurement by more than a predetermined tolerance.