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HOMESERVICE MANUALSCHEVROLET2008CHEVY EXPRESS G3500, VAN PASSENGER EXTENDEDREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 613 (HYDRAULIC BRAKE SYSTEM)DIAGNOSTIC INFORMATION AND PROCEDURESBRAKE SYSTEM VACUUM SOURCE TEST
2008 Chevrolet Chevy Express G3500, Van Passenger Extended

Brake System Vacuum Source Test

2008 Chevrolet Chevy Express G3500, Van Passenger ExtendedSECTION Brake System Vacuum Source Test
WARNING: This page is about a different car, the 2010 Cadillac STS. However, it is still accessible from the selected car via links, so may be relevant.
    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. Start the engine and allow the engine to idle until normal operating temperatures are reached.
  4. With the vehicle in PARK, the engine idling, and the air conditioning (A/C) system OFF, check to see if the engine vacuum reading is within the specified normal engine vacuum range.

    Specification:  47-68 kPa (14-20 in Hg)

  5. Turn the ignition OFF.
  6. If the engine vacuum reading was within the specified normal range, proceed to step 10.
  7. If the engine vacuum reading was 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, 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 in PARK with the A/C system OFF, until normal operating temperatures are reached.
  14. Turn the ignition OFF.
  15. Check to see if the engine vacuum reading is maintained within the specified normal engine vacuum range.

    Specification:  47-68 kPa (14-20 in Hg)

  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 the following conditions:
    • Loose connection to the vacuum brake booster
    • Deformation or contamination
    • Cracks, cuts, dry-rot
  19. If any of these conditions were found with the check valve grommet, replace the grommet.
RENDER: 1.0x

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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.