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Brake Assist System Testing

WARNING: This page is about a different car, the 2002 Oldsmobile Bravada, 2002 GMC Envoy XL, 2002 GMC Envoy, and 2002 Chevrolet TrailBlazer. 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. Inspect for proper brake pedal travel. See BRAKE PEDAL TRAVEL  under ADJUSTMENTS & INSPECTIONS. Is the brake pedal travel distance within the acceptable limits? If so, go to step  5 . If not, go to step  3
  3. Inspect for worn, missing, misaligned, bent or damaged brake pedal system components.
    • For the brake pedal pushrod component inspection, refer to BRAKE PEDAL PUSHROD  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. 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  5 .
  4. Reinspect for proper brake pedal travel. See BRAKE PEDAL TRAVEL  under ADJUSTMENTS & INSPECTIONS. Is the brake pedal travel distance within the acceptable limits? If so, go to step  8 . If not, go to next step.
  5. Check the engine vacuum source that supplies vacuum to the power brake booster. See BRAKE SYSTEM VACUUM SOURCE TEST  under SYSTEM TESTING. Is the vacuum reading within the acceptable limits? If so, go to next step. If not, check for vacuum leak.
  6. During the vacuum source inspection, did the vacuum booster check valve operate properly? If so, go to step  8 . If not, go to next step.
  7. Replace the vacuum booster check valve. See POWER BRAKE BOOSTER CHECK VALVE AND/OR HOSE  under REMOVAL & INSTALLATION. After repairs are complete, go to next step.
  8. Pump the brake pedal several times until the brake pedal becomes hard. Maintain moderate foot pressure on the brake pedal and start the engine. Observe pedal operation. Did the brake pedal drop slightly, then remain firm after the engine was started? If so, go to next step. If not, go to step  12 .
  9. Release the brake pedal. Turn the ignition OFF, then wait 15 seconds. Pump the brake pedal 2 times to check for vacuum booster available vacuum reserve. Observe pedal effort. (If operating properly, the power brake booster should maintain assist for at least 2 pedal applications.) Did the brake pedal effort increase significantly? If yes go to step  12 . If not, go to next step.
  10. Inspect the brake pedal pushrod and the brake pedal for misalignment, a bent condition and/or damage. Is the brake pedal pushrod and/or the brake pedal misaligned, bent or damaged? If so, go to next step. If not, go to step  13 .
  11. Replace the brake pedal pushrod and/or the brake pedal, as necessary. Refer to the following procedure(s). After repairs are complete, go to step  13 .
  12. Replace the power brake booster. See POWER BRAKE BOOSTER  under REMOVAL & INSTALLATION. After repairs are complete, go to next step.
  13. Install or connect any components that were removed or disconnected during diagnosis. Did you complete the operation? If so, brake assist system okay. If system is not okay, go to step  2 .
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