Note: Do not attempt to remove 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 vehicle on a level surface and perform the following operations.
2. Stop the engine so that the vacuum is released from the unit by pressing the brake pedal. Check to see if there is a noticeable difference in pedal effort after the first two or three presses.
3. Using the same force on the brake pedal, start the engine. If the unit is working properly, the pedal should move down smoothly as a vacuum builds up in the unit.
4. To check whether 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 vacuum escapes somewhere and reduces the pedal assist.
5. Start the engine again, press the brake pedal and hold it off. There should be no change in pedal stroke for thirty seconds.
6. If the vacuum booster is found to be faulty as a result of the above tests, they must be repaired.