Method for determining a degree of loading of a filter

A method for determining a degree of loading on a filter medium of a filter device on a vehicle through which a fluid flows, the method comprising:

• positioning the filter medium in a filter housing of the filter device with a filter inlet and a filter outlet;
• determining a pressure loss of the filter device between the filter inlet and the filter outlet via a differential pressure of a differential pressure switch at its switching point between a first switching state and a second switching state;
• detecting the switching state of the differential pressure switch before changing the rotary speed of the drive motor;
• if the differential pressure switch is in the first switching state, increasing a temperature of the fluid at least until the differential pressure switch switches to the second switching state;
• if the differential pressure switch is in the second switching state, changing a rotary speed of a drive motor of the vehicle at least until the differential pressure switch switches to the first switching state;
• determining an operating characteristic of the filter device based on at least the pressure loss of the filter device between the filter inlet and the filter outlet during the switching point of the differential pressure switch from the second switching state to the first switching state;
• comparing a predefined reference characteristic of the filter device with the operating characteristic;
• and
• deriving the degree of loading from a result of the comparing step.