Vacuum Brake Booster: Testing and Inspection

Brake Booster Test

NOTE: The brake booster system is assisted by an electric vacuum pump. If the electric vacuum pump system indicator stays on, check the electric vacuum pump system Initial Inspection and Diagnostic Overview before you test the brake booster. If the indicator comes on when testing the brake booster, there is no problem. Just check for and clear any DTCs with the HDS.

Functional Test

1. With the ignition switch in LOCK (0), press the brake pedal several times to deplete the vacuum reservoir, then press the brake pedal hard and hold it for 15 seconds. If the brake pedal sinks, either the master cylinder is bypassing internally or the brake system is leaking. Inspect the brake hoses and lines Testing and Inspection.

2. Start the engine with the brake pedal pressed. If the brake pedal sinks slightly, the vacuum booster is operating normally. If the brake pedal height does not vary, do the brake system test Component Tests and General Diagnostics.

Leak Test

1. Press the brake pedal with the engine running, then turn the ignition switch to LOCK (0). The brake pedal height should not vary while pressed for 30 seconds.

- If the pedal height rises, go to step 6.
- If it does not rise, go to step 2.

2. Start the engine and let it idle for 30 seconds. Turn the ignition switch to LOCK (0), and wait 30 seconds. Press the brake pedal several times using normal pressure. When the pedal is first pressed, it should be low. On consecutive applications, the pedal height should gradually rise.

- If it rises, the booster is OK.
- If it does not rise, go to step 3.

3. Disconnect the brake booster vacuum hose (A) from the 3-way joint (B). The check valve (C) is built into the hose.

NOTE: If the check valve is faulty, replace the brake booster vacuum hose/check valve as an assembly.





4. Start the engine, and let it idle. There should be vacuum available.

- If no vacuum is available, the check valve is not working properly. Replace the brake booster vacuum hose and the check valve, and retest.
- If vacuum is found, go to step 5.

5. With the ignition switch at LOCK (0), reconnect the vacuum hose to the 3-way joint.

6. Start the engine, and then pinch the brake booster vacuum hose between the 3-way joint and the booster.

7. Turn the ignition switch to LOCK (0), and wait 30 seconds. Press the brake pedal several times using normal pressure. When the pedal is first pressed, it should be low. On consecutive applications, the pedal height should gradually rise.

- If the pedal position does not vary go to step 9.
- If the pedal position varies, replace the brake booster vacuum hose/check valve (intake manifold) assembly.

8. Remove the clamp from the brake booster vacuum hose.

9. Start the engine, and pinch off the booster vacuum hose between the 3-way joint and the electric vacuum pump.

10. Turn the ignition switch to LOCK (0), and wait 30 seconds. Press the brake pedal several times using normal pressure. When the pedal is first pressed, it should be low. On consecutive applications, the pedal height should gradually rise.

- If the pedal position does not rise, inspect the seal between the master cylinder and booster. If the seal is OK, replace the brake booster.
- If the pedal position varies, inspect the vacuum hose between the 3-way joint and the electric vacuum pump check valve. If the hose is OK, replace the vacuum hose/check valve (vacuum pump).