Was the Hydraulic Brake System Diagnostic Check performed?

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Go to Step 2

Go to Hydraulic Brake Diagnostic System Check

Verify the customer complaint. Define the type of noise, and when the noise occurs. Refer to Hydraulic Booster Noise Diagnosis .

Is the hydraulic booster making a moan or low frequency hum?

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Go to Step 3

Go to Step 4

The noise may be the result of a problem within the power steering system. Refer to Power Steering System Test in Power Steering System.

Was a repair performed on the power steering system?

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Go to Step 8

Go to Step 4

Check the hydraulic brake booster accumulator for proper operation. Refer to Accumulator Leak-Down Test .

Is the hydraulic brake booster accumulator operating properly?

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Go to Step 5

Go to Step 6

1. Obtain a vehicle with a known acceptable brake booster system.
2. Run both vehicles until the engines reach normal operating temperature.
3. In both vehicles, duplicate the operating condition associated with the noise. Listen for the noise.
4. Compare the results.

Does the acceptable system make the same noise?

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Go to Hydraulic Brake Diagnostic System Check

Go to Step 7

Replace the accumulator. Refer to Hydraulic Brake Booster Accumulator Replacement .

Is the repair complete?

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Go to Step 8

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

Is the repair complete?

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Go to Step 8

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Verify proper brake system operation.

Does the original condition still exist?

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Verify customer complaint. Begin the diagnosis again. Go to Step 1.

Go to Hydraulic Brake Diagnostic System Check