Diagnostic function

• The vacuum sensor is used to check whether the pressure in the system has fallen below a certain value in a certain time.
• As soon as the brake pedal is released, the pump output is calculated based on the engine speed and subtracted from the work to be performed in order to bring the absolute pressure below a certain threshold.
• It is not important here whether the connected solenoid change-over valves were actuated at the time of the diagnostic test.
• The >Vacuum system< system test in the PIWIS Tester can be used for complete testing of the vacuum system, because all solenoid switchover valves are forcibly actuated at the time of the diagnostic test in this case.

INFORMATION 

1. The system includes:
   • Mechanical vacuum pump
   • Brake booster
   • Vacuum check valve
   • Coolant shutoff valve and relevant solenoid change-over valve, respectively for:
   • Heat exchanger for heating
   • Engine (short-circuit loop)
   • Heat exchanger for transmission oil
   • Heat exchanger for clutch fluid (PDK only)
   • Vacuum unit and relevant solenoid change-over valve, respectively for:
     • Variable intake manifold (tuning flap)
     • Air cleaner flap
     • Exhaust flap
     • Acoustic simulator
     • Variable intake manifold 2 (Power Kit X51)
     • Diverter valve (Turbo)
   • Vacuum lines to all components mentioned above
2. There may be several small leaks, which correspond in total to the leak determined here.