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For 1990-2009 cars only

Hydraulic Booster Diagnosis Erratic Operation

Erratic Hydraulic Brake Booster Operation

Step

Action

Value(s)

Yes

No

DEFINITION: Brake pedal sticks, binds, or grabs.

1

  1. Run the engine at a fast idle.
  2. Pull the brake pedal rearward with 44 N (10 lb) of force. Release the pedal.
  3. Measure the distance from the pedal to the floor board.
  4. Apply the brakes with 444 N (100 lb) of force.
  5. Release the pedal. Measure the distance from the pedal to the floor board.

Did the pedal return to the same position?

--

Go to Step 3

Go to Step 2

2

The brake pedal is sticking or binding. Repair the pedal as necessary.

Is the repair complete?

--

Go to Step 9

--

3

Do the brakes self-apply?

--

Go to Step 4

The condition is intermittent. Re-verify the condition. Go to Step 1

4

  1. Inspect the return hose between the hydraulic booster and the power steering pump reservoir for and obstruction, or kinked connections.
  2. Remove the obstruction, or replace the hose as necessary.

Verify the repair. Is the condition still present?

--

Go to Step 5

System OK

5

  1. Remove the cover from the master cylinder reservoir.
  2. Rapidly apply the brake pedal 3 cm (1 in), observing the brake fluid in the reservoir.

Does the fluid surface in the forward reservoir show movement, or spouting?

--

The condition is intermittent. Re-verify the condition. Go to Step 1

Go to Step 6

6

The hydraulic booster or the master cylinder is faulty. Determine if the master cylinder is faulty. Refer to Master Cylinder Diagnosis .

Is the master cylinder faulty?

--

Go to Step 7

Go to Step 8

7

Repair or replace the master cylinder as necessary. Refer to Master Cylinder Overhaul .

Is the repair complete?

--

Go to Step 9

--

8

Repair or replace the hydraulic booster as necessary. Refer to Power Brake Booster Replacement .

Is the repair complete?

--

Go to Step 9

--

9

Verify the repair.

Is the condition still present?

--

Begin the diagnosis again. Go to Step 1

System OK

Hydraulic Booster Diagnosis Excessive Effort

Step

Action

Value(s)

Yes

No

1

  1. With the engine OFF, apply and release the brake pedal four times. This will relieve pressure in the hydraulic booster.
  2. Apply the pedal. Maintain light pressure on the pedal.
  3. Start the engine.

If the power section is operating, holding the pedal requires less pressure. The pedal will fall slightly, then hold.

Did the pedal fall slightly, then hold?

--

Go to Step 2

Go to Step 7

2

  1. Accelerate the engine to medium speed.
  2. Apply the brake pedal with 444 N (100 lb) for no more than 5 seconds.
  3. Stop the engine. This will stop the power steering pump.
  4. Wait 90 seconds.
  5. Repeatedly apply the brakes.

Are two or more brake applications power assisted?

--

Go to Step 3

Go to Step 6

3

The accumulator is functioning properly. Perform the following test.

  1. Thoroughly clean the hydraulic booster and all of the hose connections.
  2. Start the engine. Run the engine at idle speed.
  3. Apply the brake pedal with 444 N (100 lb).
  4. Important: Do not hold the brake pedal with 444 N (100 lb) for more than 5 seconds at a time.

  5. Maintain the pressure on the brake pedal while inspecting the hydraulic booster and hose connections for leaks.

Did you find any leaks?

--

Go to Step 17

Go to Step 4

4

  1. Apply and release the brake pedal several times.
  2. Apply 110-155 N (25-35 lb). Maintain the pressure.

Does the brake pedal fall away?

--

Go to Step 5

 

5

The hydraulic brake system is leaking. Refer to Brake Fluid Leak .

Did you find and correct the condition?

--

Go to Step 18

--

6

Repair or replace the hydraulic booster.

Is the procedure complete?

--

Go to Step 18

--

7

Check the fluid level of the power steering pump reservoir.

Is the fluid level correct?

--

Go to Step 8

Go to Step 15

8

Check the drive belt for wear and incorrect tension. Refer to Drive Belt Diagnosis .

Did you find and correct a problem?

--

Go to Step 18

Go to Step 9

9

Check the power steering pump speed.

Is the pump speed slow?

--

Go to Step 10

--

10

  1. Adjust the power steering pump speed.
  2. Repeat the Basic Test, refer to Step 1.

Did you find and correct a problem?

--

Go to Step 18

Go to Step 11

11

Perform the Power Steering Pump Flow and Relief Pressure Test. Refer to Power Steering System Test in Power Steering System.

Is the pump output within specifications?

--

Go to Step 14

Go to Step 12

12

Is the pump output low?

--

Go to Step 13

 

13

  1. Replace the pump.
  2. Repeat the Basic Test, refer to Step 1.

Is the procedure complete?

--

Go to Step 18

--

14

Repair or replace the hydraulic booster. Refer to Power Brake Booster Replacement

Is the procedure complete?

--

Go to Step 18

--

15

Is the power steering pump reservoir fluid level low?

--

Go to Step 16

 

16

  1. Add fluid.
  2. Repeat the Basic Test, refer to Step 1.
  3. Thoroughly clean the hydraulic booster and all of the hose connections.
  4. Start the engine. Run the engine at idle speed.
  5. Apply the brake pedal with 444 N (100 lb).
  6. Important: Do not hold the brake pedal with 444 N (100 lb) for more than 5 seconds at a time.

  7. Maintain the pressure on the brake pedal while inspecting the hydraulic booster and hose connections for leaks.

Did you find any leaks?

--

Go to Step 17

--

17

Repair or replace any leaking components.

Is the procedure complete?

--

Go to Step 18

--

18

Verify the repair.

Does the original condition still exist?

--

Begin the diagnosis again. Go to Step 1

System OK

Hydraulic Booster Diagnosis General Diagnosis

Slow Brake Pedal Return

Checks

Action

Check for excessive seal friction in the booster.

Overhaul the booster. Use a new seal kit.

Check for faulty spool action.

Flush the steering system while pumping the brake pedal.

Check for a restriction in the return hose from the booster to the pump reservoir.

Replace the hose.

Check for a damaged input rod end.

Replace the input rod. Replace the piston assembly.

The Brakes Grab--the Hydraulic Booster Chatters--the Pedal Vibrates

Checks

Action

Check for faulty spool action, caused by contamination.

Flush the steering system while pumping the brake pedal.

Check the power steering pump belt for slippage.

Refer to Drive Belt Diagnosis .

Check for a low fluid level in the power steering pump.

Fill the reservoir. Check for external leaks.

The Accumulator Leak-down System Does Not Hold a Charge

Checks

Action

Check for contamination in the steering system.

Flush the steering system while pumping the brake pedal.

Check for contamination in the booster system.

Flush the steering system while pumping the brake pedal.

Check for internal leakage in the accumulator system.

Overhaul the accumulator. Use a rebuild kit and a seal kit.

The Brakes Self-apply (When You Turn the Steering Wheel)

Checks

Action

Check for contamination in the steering system.

Replace the hydraulic booster. Flush the complete system.

Check for contamination in the booster system.

Replace the hydraulic booster. Flush the complete system.

Check for a restriction in the return hose from the booster to the pump reservoir.

Replace the hose.