Brake System Vacuum Source Test

Brake System Vacuum Source Test

Note:

* Engine temperature, accessory load, and elevation level will affect engine vacuum.

* Vacuum readings will decrease by approximately 2.7 kPa (0.8 in Hg) for every 305 m (1000 ft) of elevation above sea level.

1. Disconnect the engine vacuum hose from the vacuum brake booster check valve.

2. Install a vacuum gauge to the engine vacuum hose.

3. Install a scan tool to the vehicle.

4. Start the engine and allow the engine to idle until normal operating temperatures are reached.

Note:
To obtain the gauge pressure from the manifold absolute pressure (MAP) sensor, subtract the absolute pressure of the MAP sensor from atmospheric pressure.

5. With the vehicle in PARK or NEUTRAL with the park brake on, the engine idling, and the air conditioning (A/C) system OFF, check to see if the engine vacuum reading is the gauge pressure calculated from the pressure of the MAP sensor indicated on the scan tool.

6. Turn the ignition OFF.

7. If the engine vacuum reading is within the specified normal range, proceed to step 11.

8. If the engine vacuum reading is NOT within the specified normal range, inspect the engine vacuum hose for the following conditions.

* Loose connection to the engine

* Collapse, deformation or contamination

* Cracks, cuts, or brittleness

9. If any of these conditions were found with the engine vacuum hose, replace the hose, then repeat steps 2-5.

10. If none of these conditions were found with the engine vacuum hose, then there is an engine vacuum source problem, check the engine vacuum system.

11. Remove the vacuum brake booster check valve from the booster.

12. Install the check valve to the engine vacuum hose.

13. Install the vacuum gauge to the check valve.

14. Start the engine and allow the engine to idle in park or neutral with the park brake on and with the A/C system OFF, until normal operating temperatures are reached.

15. Turn the ignition OFF.

Note:
To obtain the gauge pressure from the manifold absolute pressure (MAP) sensor, subtract the absolute pressure of the MAP sensor from atmospheric pressure.

16. Visually inspect the engine vacuum reading is maintained at the same gauge pressure as the pressure obtained form the MAP sensor as indicated on the scan tool.

17. If the engine vacuum reading is maintained within the specified normal range, proceed to step 19.

18. If the engine vacuum reading is NOT maintained within the specified normal range, replace the vacuum brake booster check valve, then repeat steps 12-16.

19. Inspect the vacuum brake booster check valve grommet for the following conditions:

* Loose connection to the vacuum brake booster

* Deformation or contamination

* Cracks, cuts or brittleness

20. If any of these conditions were found with the check valve grommet, replace the grommet.