LEMON Manuals: Even more car manuals for everyone: 1960-2025
Home >> Hummer >> 2003 >> H2 >> Repair and Diagnosis >> External Pages >> Different car >> Section 197 (Disc Brakes) >> System Tests >> Brake System Vacuum Source Test
April 5, 2026: LEMON Manuals is launched! Read the announcement.

Brake System Vacuum Source Test

WARNING: This page does not describe the selected car, but rather 12 other vehicles, including the 2003 GMC Yukon XL, 2003 GMC Yukon, 2003 GMC Sierra, 2003 GMC Cab & Chassis Sierra, and 2003 Chevrolet Tahoe. However, it is still accessible from the selected car via links, so may be relevant.
  1. Disconnect the engine vacuum hose from the vacuum brake booster check valve.
  2. Install a vacuum gauge to the engine vacuum hose.
  3. Start the engine and allow the engine to idle until normal operating temperatures are reached.
  4. Check to see if the engine vacuum reading is within the normal engine vacuum range of 14-20 in. Hg (47-68 kPa).
  5. Turn the ignition off.
  6. If the engine vacuum reading is within the specified normal range, proceed to step  10.
  7. If the engine vacuum reading is NOT within the specified normal range, inspect the engine vacuum hose for a tight connection to the engine, collapse, deformation or contamination, cracks, cuts or dry-rot.
  8. If any of these conditions were found with the engine vacuum hose, replace the hose, then repeat steps  2- 4 .
  9. 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.
  10. Remove the vacuum brake booster check valve from the booster.
  11. Install the check valve to the engine vacuum hose.
  12. Install the vacuum gauge to the check valve.
  13. Start the engine and allow the engine to idle until normal operating temperatures are reached.
  14. Turn the ignition off.
  15. Check to see if the engine vacuum reading is maintained within the normal engine vacuum range of 14-20 in. Hg (47-68 kPa).
  16. If the engine vacuum reading is maintained within the specified normal range, proceed to step  18.
  17. If the engine vacuum reading is NOT maintained within the specified normal range, replace the brake booster check valve, then repeat steps  11- 15 .
  18. Inspect the brake booster check valve grommet for a firm connection to the vacuum brake booster, deformation or contamination, cracks, cuts or dry-rot.
  19. If any of these conditions were found with the check valve grommet, replace the grommet.
scientia non olet · About LEMON Manuals