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Brake Assist System Diagnosis

WARNING: This page is about a different car, the 2002 GMC Sierra, 2002 GMC Cab & Chassis Sierra, 2002 Chevrolet Silverado, and 2002 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.
NOTE: This diagnostic procedure is designed to diagnose only the components of the brake assist system in order to determine if the brake assist system is operating properly.
  1. Were you sent here from a brake symptom? If so, proceed to next step. If not, see DIAGNOSTIC STARTING POINT  .
  2. Is the symptom related to brake system noise? If so, go to step  4 . If not, proceed 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. Did the noise inspection indicate a concern with the power steering system drive belt? If so, proceed to next step. If not, go to step  6 .
  5. Replace the power steering system drive belt. When complete, proceed to next step.
  6. Did the noise inspection indicate a possible restriction in the hydraulic brake booster power steering system return hose? If so, proceed to next step. If not, go to step  8 .
  7. Replace the restricted hydraulic brake booster power steering return hose. See appropriate POWER RECIRCULATING ball article in STEERING. When complete, proceed to next step.
  8. During the noise inspection, did the hydraulic brake booster produce abnormal noises? If so, go to step  14 . If not, proceed to next step.
  9. Inspect for proper brake pedal travel. See BRAKE PEDAL TRAVEL MEASUREMENT & INSPECTION  under ADJUSTMENTS & INSPECTION. Is the brake pedal travel distance within the acceptable limits? If so, go to step  12 . If not, proceed 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 & INSPECTION. 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. See BRAKE PEDAL ASSEMBLY  or HYDRAULIC BRAKE BOOSTER  under REMOVAL & INSTALLATION. Did you find and replace any worn, missing, misaligned, bent or damaged brake pedal system components? If so, proceed to next step. If not, go to step  12 .
  11. Reinspect for proper brake pedal travel. See BRAKE PEDAL TRAVEL MEASUREMENT & INSPECTION  under ADJUSTMENTS & INSPECTION. Is the brake pedal travel distance within the acceptable limits? If so, go to step  14 . If not, proceed to next step.
  12. Inspect the power steering drive belt for conditions which could cause slipping. Replace the power steering drive belt if necessary. Check the power steering system fluid level and adjust the level if necessary. See appropriate POWER RECIRCULATING ball article in STEERING. When complete, proceed to next step.
  13. With the ignition OFF, depress the brake pedal 4 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, proceed to next step.
  14. Inspect the power steering system pressure supplying the hydro-boost unit. See appropriate POWER RECIRCULATING ball article in STEERING. Replace power steering components as indicated by the results of the pressure analysis. Did you find and correct a condition? If so, proceed to next step. If not, go to step  19 .
  15. With the ignition OFF, depress the brake pedal 4 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, proceed 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, proceed to next step.
  17. Release the brake pedal. Start the engine to pressurize the system. Turn the ignition off. Wait one hour, then depress the brake pedal 4 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 4th time? If so, proceed 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. When complete, go to step  20 .
  19. Replace the hydraulic brake booster assembly. See HYDRAULIC BRAKE BOOSTER  under REMOVAL & INSTALLATION. When complete, proceed to next step.
  20. Install or connect any components that were removed or disconnected during diagnosis. The brake assist system is okay.
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