If the vacuum at the air filter outlet is too high, the CDI control unit (N3/9) generates a signal to turn on the instrument cluster indicator light (A1e27) "Air filter dirty".
VN 9.034 1. Filter outlet duct; 2. Air filter outlet pressure sensor (B2S/5)
Air pressure acts on the diaphragm (C), causing the piezoresistors to change their resistance. The change in the sensor output voltage is recorded by the CDI control unit (N3/9).
VN 9.035 1. Body; 2. Supply of the measured pressure; 3. Diaphragm; 4. Air filter outlet pressure sensor (B28/5)