Checking Brake Booster

1. Connect a battery charger with a current rating of at least 40 A  to the jump-start terminals in the engine compartment.
2. Switch on ignition.
3. PIWIS Tester II 9818  with the current software version installed must be connected to the vehicle communication module (VCI) via the USB cable  . Then, connect the communication module to the vehicle and switch on the PIWIS Tester.
4. On the PIWIS Tester start screen, call up the => 'Diagnostics  ' menu and select the vehicle type => 'Macan  '.

The diagnostic application is then started and the control unit selection screen is populated.

1. Select the control unit => 'PSM  ' in the control unit selection screen (=> 'Overview  ' menu) and press [>>] to confirm your selection → see figure  .

   Control unit selection 

2. Press [F11] to skip the question as to whether you want to create a vehicle analysis log (VAL).
3. Press [>>] to acknowledge the message that may appear informing you that campaigns for the vehicle are stored in the PIWIS information system.
4. Once the PSM control unit has been found and is displayed in the overview, select the => 'Actual values/input signals  ' menu → see figure  .
5. In the 'Actual values/input signals' menu, highlight the sensors to be checked => 'Brake pressure (hydraulic unit sensor)  ' and => 'Brake booster vacuum (vacuum sensor)  ' and press F12 to confirm.
6. Start the engine in selector-lever position "P" and leave it running for approx. 30 seconds at idle speed until the 'Vacuum  ' is no longer increasing and remains constant.
   NOTE:

   At sea level  , a vacuum  of at least 900 mbar  must be reached at idle speed in the brake booster. The higher the position  above sea level, the lower  the ambient pressure, and thus the lower the vacuum to be reached  in the brake booster.

   The vacuum in the brake booster drops by approx. 10 mbar for every 100 m increase in height  .

   This means, for example, that a vehicle at 1, 000 m  above sea level still only reaches a vacuum of at least 800 mbar  in the brake booster.

7. Set the measured value for 'Brake pressure  ' to approx. 130 bar  by pressing the brake pedal, keep the brake pressure at approx. 130 bar for 5 seconds  and check the displayed measured values → see figure  .

   Measured values 

   • If the vacuum drops by less than approx. 100 mbar  from the starting value after setting the brake pressure  and then increases again  or remains constant, the brake booster is OK  . Continue with Step 8  .
   • If the vacuum drops quickly by more than approx. 100 mbar from the starting value  when checking the brake booster  , the brake booster must be replaced  .
8. Stop the engine and switch off the ignition.
9. Disconnect the PIWIS Tester from the vehicle.
10. Switch off and disconnect the battery charger.