S4 - Booster Leak Check

- Key ON.

- Run engine until vacuum reaches 51-64 kPa (15-19 in-Hg).

- Key OFF.

- Push down on the brake pedal and hold for a few seconds and release.

- Does the vacuum drop to 0 kPa (0 in-Hg)?

YES -- Replace or Rebuild power brake booster as required.

NO -- System checks OK. Remove vacuum gauge and reconnect all vacuum lines.