Note: Do not attempt to dismantle the unit, clean or replace the air filter, or adjust the length of the unit rod. The unit is sealed and no components are accessible for repair.
1. Any failure of the vacuum booster will be obvious to the driver, due to the increased pedal force required to achieve normal braking. To check the unit, place the car on a level surface and perform the following operations.
2. Turn off the engine to release the vacuum from the block by pressing the brake pedal. Check if there is a noticeable difference in pedal force after the first two or three presses.
3. With the same force on the brake pedal, start the engine. If the unit is working properly, the pedal should move down smoothly, since a vacuum is created in the unit.
4. To check if the unit is completely sealed, start the engine and after one or two minutes turn off the ignition. Press the brake pedal with the same force. If the unit is sealed, the pedal should drop to normal height on the first press, but then the height should gradually rise as the vacuum escapes somewhere and reduces the assistance when pressing.
5. Start the engine again, press the brake pedal and hold it with the engine off. There should be no change in pedal travel for thirty seconds.
6. If the vacuum booster is found to be faulty as a result of the above tests, it must be rectified.