Checking Brake Booster (Low-Pressure Test)

- Pull hose off connection. Install vacuum tester 34 3 100 between connection and vacuum hose on non-return valve.
- Start engine.
- Check buildup of partial vacuum.
- Switch off engine.
- Press brake pedal to set a partial vacuum of no more than 0.8 bar and wait for value to stabilize.
- When the brake pedal is not pressed, the partial vacuum is allowed to drop by max. 0.06 bar over a test period of 1 minute.

If specified values are not reached:
- Check line connections for vacuum seal.
- Replace vacuum non-return valve.
- Check seal between brake booster and brake master cylinder (sealing ring) for perfect condition and correct seating.
- If the specified values are not achieved when the test is repeated, you must replace the brake booster.