Audi A3  Controls and displays  Instruments and warning/indicator lamps  Warning and indicator lamps
Particulate filter: system fault. See owner's manual
The diesel particulate filter requires regeneration. You can assist the self-cleaning function of the filter by driving as follows:
Drive at a speed of at least 60 km/h for about 15 minutes in 4th or 5th gear, or with the selector lever in position S on vehicles with automatic gearbox. Keep the engine speed at about 2000 rpm. As a result of the increase in temperature, the soot in the filter will be burned off. The indicator lamp will go out once the cleaning process has been completed successfully.
If the indicator lamp does not go out, drive to a qualified workshop without delay and have the fault rectified.
It is essential that you adjust your speed to suit the weather, road, terrain and traffic conditions. The recommended driving speed must never lead to the driver disregarding the traffic regulations.
For more information about the diesel particulate filter, refer to Link.

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