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Brake Assist System Testing

WARNING: This page does not describe the selected car, but rather 6 other vehicles, including the 2003 GMC Savana Special, 2003 GMC Savana Camper Special, 2003 GMC Savana, 2003 Chevrolet RV Cutaway, and 2003 Chevrolet Cutaway. However, it is still accessible from the selected car via links, so may be relevant.
  1. Were you sent here from DIAGNOSTIC STARTING POINT - HYDRAULIC BRAKE? If so, go to next step. If not, see DIAGNOSTIC STARTING POINT - HYDRAULIC BRAKE  under TROUBLE SHOOTING.
  2. Is the symptom related to brake system noise? If so, go to step  4 . If not, go to next step.
  3. Is the symptom related to the brake system self-applying when the steering wheel is being turned? If so, go to step  14 . If not, go to step  9 .
  4. Check the hydraulic assist system operation for the presence of abnormal noise. See HYDRAULIC BRAKE ASSIST NOISE INSPECTION  under ADJUSTMENTS & INSPECTIONS. Did the noise inspection indicate a concern with the power steering system drive belt? If so, go to next step. If not, go to step  6 .
  5. Replace the power steering system drive belt. See appropriate COOLING SYSTEMS - MECHANICAL article in ENGINE. Did you complete the replacement? If so, go to next step.
  6. Did the noise inspection indicate a possible restriction in the hydraulic brake booster power steering system return hose? If so, go to next step. If not, go to step  8 .
  7. Replace the restricted hydraulic brake booster power steering return hose. See appropriate POWER STEERING article in STEERING SYSTEMS. Did you complete the replacement? If so, go to next step.
  8. During the noise inspection, did the hydraulic brake booster produce abnormal noises? If so, go to step  14 . If not, go to next step.
  9. Inspect for proper brake pedal travel. See BRAKE PEDAL TRAVEL MEASUREMENT & INSPECTION  under ADJUSTMENTS & INSPECTIONS. Is the brake pedal travel distance within the acceptable limits? If so, go to step  12 . If not, go to next step.
  10. Inspect for worn, missing, misaligned, bent or damaged brake pedal system components.
    • For the brake pedal pushrod component inspection, see BRAKE PEDAL PUSHROD INSPECTION  under ADJUSTMENTS & INSPECTIONS.
    • Inspect the brake pedal bushings for excessive wear and/or damage and inspect the brake pedal for a misaligned, bent and/or damaged condition.
    Replace the brake pedal system components that are worn, missing, misaligned, bent or damaged, refer to the following procedures as necessary. See BRAKE PEDAL ASSEMBLY  and HYDRAULIC BRAKE BOOSTER  under REMOVAL & INSTALLATION. Did you find and replace any worn, missing, misaligned, bent or damaged brake pedal system components? If so, go to next step. If not, go to step  12 .
  11. Reinspect for proper brake pedal travel. See BRAKE PEDAL TRAVEL MEASUREMENT & INSPECTION  under ADJUSTMENTS & INSPECTIONS. Is the brake pedal travel distance within the acceptable limits? If so, go to step  14 . If not, go to next step.
  12. Inspect the power steering drive belt for conditions which could cause slipping. Replace the power steering drive belt if necessary. See appropriate COOLING SYSTEM - MECHANICAL article in ENGINES. Check the power steering system fluid level and adjust the level if necessary. See appropriate FLUID CHECK in POWER STEERING article. Did you complete the operations? If so, go to next step.
  13. With the ignition OFF, depress the brake pedal four times or until the effort required to apply the pedal increases significantly. Maintain moderate foot pressure on the brake pedal and start the engine. Observe pedal operation. Did the brake pedal fall slightly, then hold after the engine was started? If so, go to step  16 . If not, go to next step.
  14. Inspect the power steering system pressure supplying the hydro-boost unit. See appropriate POWER STEERING SYSTEM TEST in POWER STEERING SYSTEM article. Replace power steering components as indicated by the results of the pressure analysis. Did you find and correct a condition? If so, go to next step. If not, go to step  19 .
  15. With the ignition OFF, depress the brake pedal four times or until the effort required to apply the pedal increases significantly. Maintain moderate foot pressure on the brake pedal and start the engine. Observe pedal operation. Did the brake pedal fall slightly, then hold after the engine was started? If so, go to next step. If not, go to step  19 .
  16. Release the brake pedal. Allow the engine to continue to idle in order to pressurize the system. Turn the ignition OFF. Wait 90 seconds, then depress the brake pedal 2 times to check for hydraulic brake booster immediate reserve. Observe pedal effort. Did the brake pedal apply effort significantly increase when the brake pedal was applied the second time? If so, go to step  19 . If not, go to next step.
  17. Release the brake pedal. Start the engine to pressurize the system. Turn the ignition OFF. Wait 1 hour, then depress the brake pedal four times to check for hydraulic brake booster accumulator reserve leak-down. Observe pedal effort. Did the brake pedal apply effort significantly increase when the brake pedal was applied the fourth time? If so, go to next step. If not, go to step  20 .
  18. Replace the hydraulic brake booster accumulator assembly. See HYDRAULIC BRAKE BOOSTER ACCUMULATOR  under REMOVAL & INSTALLATION. Did you complete the replacement? If so, go to step  20 .
  19. Replace the hydraulic brake booster assembly. See HYDRAULIC BRAKE BOOSTER  under REMOVAL & INSTALLATION. Did you complete the replacement? If so, go to next step.
  20. Install or connect any components that were removed or disconnected during diagnosis. Did you complete the operation? If so, system is okay. Is system is not okay, go to step  2 .
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