DEFINITION: This diagnostic table is designed to diagnose ONLY the components of the brake ASSIST system in order to determine if the brake ASSIST system is operating properly. You will be directed by the appropriate Symptom Table to go to other brake system diagnostic tables as appropriate.

Were you sent here from a Brake Symptom Table?

Go to Step 2

Go to Diagnostic Starting Point - Hydraulic Brakes

Is the symptom related to brake system noise?

Go to Step 4

Go to Step 3

Is the symptom related to the brake pedal travel feel?

Go to Step 12

Return to Symptom Table

Check the hydraulic assist system operation for the presence of abnormal noise. Refer to Hydraulic Brake Assist System Noise Inspection .

Did the noise inspection indicate a concern with the power brake booster pump dampers?

Go to Step 5

Go to Step 6

Replace the power brake booster pump dampers. Refer to Power Brake Booster Replacement .

Did you complete the replacement?

Go to Step 6

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Did the noise inspection indicate a possible restriction in the power brake booster inlet hose?

Go to Step 7

Go to Step 8

Replace the restricted power brake booster inlet hose. Refer to Power Brake Booster Inlet Hose Replacement .

Did you complete the replacement?

Go to Step 8

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Did the noise inspection indicate a possible restriction in the power brake booster outlet pipe?

Go to Step 9

Go to Step 10

Replace the restricted power brake booster outlet pipe. Refer to Power Brake Booster Outlet Front Pipe Replacement .

Did you complete the replacement?

Go to Step 10

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During the inspection, did the hydraulic brake booster pump and motor make abnormal noises?

Go to Step 11

Go to Step 9

Replace the hydraulic brake booster assembly. Refer to Power Brake Booster Replacement .

Did you complete the replacement?

Go to Step 20

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Inspect for proper brake pedal travel. Refer to Brake Pedal Travel Measurement and Inspection .

Is the brake pedal travel distance within the acceptable limits?

Go to Step 12

Go to Step 13

1. Inspect for worn, missing, misaligned, bent, or damaged brake pedal system components.

•	For the brake pedal pushrod component inspection, refer to Brake Pedal Pushrod Inspection .

•	Inspect the brake pedal clevis for excessive wear and/or damage and inspect the brake pedal for a misaligned, bent, and/or damaged condition.

2. Replace the brake pedal system components that are worn, missing, misaligned, bent, or damaged. Refer to the following procedures as necessary.

•	Brake Pedal Assembly Replacement

•	Master Cylinder Replacement for a bent or damaged pedal pushrod replacement

Did you find and replace any worn, missing, misaligned, bent, or damaged brake pedal system components?

Go to Step 14

Go to Step 15

Reinspect for proper brake pedal travel. Refer to Brake Pedal Travel Measurement and Inspection .

Is the brake pedal travel distance within the acceptable limits?

Go to Step 16

Go to Step 15

Check for air trapped in the hydraulic booster pump and motor assembly. Refer to Hydraulic Brake System Bleeding .

Did you complete the hydraulic brake system bleeding procedure?

Go to Step 16

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1. With the ignition OFF, depress the brake pedal 20 times or until the brake pedal stroke increases.
2. Maintain moderate foot pressure on the brake pedal and start the engine. Observe pedal operation.

Did the brake pedal push back, then hold after the engine was started?

Go to Step 17

Go to Step 19

1. Release the brake pedal.
2. Start the engine to pressurize the system.
3. Turn the ignition OFF.
4. Wait 1 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 fourth time?

Go to Step 18

Go to Step 20

Replace the hydraulic brake booster accumulator assembly. Refer to Power Brake Booster Pump Fluid Accumulator Replacement .

Did you complete the replacement?

Go to Step 20

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Replace the pump and motor assembly. Refer to Power Brake Booster Replacement .

Did you complete the replacement?

Go to Step 20

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Install or connect any components that were removed or disconnected during diagnosis.

Did you complete the operation?

Brake Assist System OK

Return to Symptom Table

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