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Brake Assist Diagnosis

WARNING: This page is about a different car, the 2003 Pontiac Aztek and 2003 Buick Rendezvous. However, it is still accessible from the selected car via links, so may be relevant.
  1. Were you sent here from a Symptom Test? If so, go to next step. If not, go to GENERAL DIAGNOSIS  under TROUBLE SHOOTING.
  2. Inspect for proper brake pedal travel. See BRAKE PEDAL TRAVEL MEASUREMENT & INSPECTION  under BRAKE PEDAL in ADJUSTMENTS & INSPECTION. Is the brake pedal travel distance within the acceptable limits? If so, go to step  5. If not, go to next step.
  3. 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 BRAKE PEDAL in 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, 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 MEASUREMENT & INSPECTION  under BRAKE PEDAL in ADJUSTMENTS & INSPECTION. 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 vacuum brake booster. See BRAKE VACUUM SOURCE TEST  under SYSTEM TESTS. Is the vacuum reading within the acceptable limits? If so, go to next step. If not, diagnose and repair low engine vacuum.
  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 VACUUM BRAKE BOOSTER CHECK VALVE AND/OR HOSE  under REMOVAL & INSTALLATION. After completing the replacement, 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, the 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 vacuum brake booster should maintain assist for at least 2 pedal applications.) Did the brake pedal effort increase significantly? If so, 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 completing the replacement, go to step  13.
  12. Replace the vacuum brake booster. VACUUM BRAKE BOOSTER  under REMOVAL & INSTALLATION. After completing the replacement, go to next step.
  13. Install or connect any components that were removed or disconnected during diagnosis. After completing the operation, the system should be okay.
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