Brake Assist System Test
- If sent here from SYMPTOM INDEX table, go to next step. If not sent here from SYMPTOM INDEX table, perform HYDRAULIC BRAKE DIAGNOSTIC SYSTEM CHECK under TROUBLE SHOOTING.
- Inspect for proper brake pedal travel. See BRAKE PEDAL TRAVEL under ADJUSTMENTS & INSPECTIONS. If the brake pedal travel distance is within the acceptable limits, go to step 5. If the brake pedal travel distance is not within the acceptable limits, go to next step.
- Perform the following:
- 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.
If any worn, missing, misaligned, bent or damaged brake pedal system components were found and corrected, go to next step. If problem was not found, go to step 5.
- Reinspect for proper brake pedal travel. See BRAKE PEDAL TRAVEL under ADJUSTMENTS & INSPECTIONS. If the brake pedal travel distance is within the acceptable limits, go to step 8. If the brake pedal travel distance is not within the acceptable limits, go to next step.
- Check the engine vacuum source that supplies vacuum to the vacuum brake booster. See BRAKE SYSTEM VACUUM SOURCE TEST under SYSTEM TESTS. If the vacuum reading is within the acceptable limits, go to next step. If the vacuum reading is not within the acceptable limits, see ENGINE MECHANICAL article in ENGINES.
- During the vacuum source inspection, if the vacuum booster check valve operates properly, go to step 8. If the vacuum booster check valve does not operate properly, go to next step.
- Replace the vacuum booster check valve. See VACUUM BRAKE BOOSTER CHECK VALVE under REMOVAL & INSTALLATION. After replacement, go to next step.
- 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. If the brake pedal drops slightly, then remains firm after the engine was started, go to next step. If the brake pedal is not as specified, go to step 12.
- 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. If the brake pedal effort increases significantly, go to step 12. If the brake pedal effort does not increase significantly, go to next step.
- Inspect the brake pedal pushrod and the brake pedal for misalignment, a bent condition and/or damage. If the brake pedal pushrod and/or the brake pedal is misaligned, bent or damaged, go to next step. If problem is not found, go to step 13.
- Replace the brake pedal pushrod and/or the brake pedal, as necessary. Refer to the following procedure(s).
After replacement, go to step 13.
- Replace the vacuum brake booster. See VACUUM BRAKE BOOSTER under REMOVAL & INSTALLATION. After replacement, go to next step.
- Install or connect any components that were removed or disconnected during diagnosis. If procedure is completed, the brake assist system is okay. Go to SYMPTOM INDEX table.