If the vacuum at the outlet of the air filter is too high, then the CDI control unit (N3/9) generates an ignition signal for the indicator light of the instrument cluster (A1e27) ''The air filter is dirty*.
VN 9.034 1. Outlet air duct filter; 2. Air filter outlet pressure sensor (B2S/5)
Air pressure acting on the diaphragm (WITH). In this case, the piezoresistors change their resistance. The change in the output voltage of the sensor is registered by the CDI control unit (N3/9).
VN 9.035 1. Housing; 2. Supply of measured pressure; 3. Aperture; 4. Air filter outlet pressure sensor (Q28/5)