Hydraulic Booster Noise Diagnosis

SYSTEM TESTS
The hydraulic booster uses fluid pressure from the power steering system. A malfunctioning power steering system can affect the hydraulic booster. A malfunctioning booster can affect the steering system. Perform the following procedure before beginning any extensive testing.
1. Inspect all of the power steering and the brake pipe connections for leaks and restrictions.

NOTICE: Power steering fluid and brake fluid cannot be mixed. If brake seals contact power steering fluid or steering seals contact brake fluid, seal damage will result.

2. Ensure that the master cylinder is properly filled.
3. Ensure that the power steering pump reservoir is properly filled.
If the power steering fluid contains air, bleed the power steering system.
4. Inspect the power steering pump belt for wear and improper tension.
5. Test the power steering pump pressure.





Noise from the relief valve is normal when applying the brakes. Firmly applying the brake pedal while the vehicle is parked also causes noise. The noises are the result of air allowed into the fluid during these conditions. The air remains in the fluid only temporarily.
Power steering pump noise can be confused with transmission, rear axle, or generator noise.
The following noises come from the hydraulic booster.
The noises may be cause for a customer concern. Noises may be normal and temporary. Noises may be a sign of wear, or evidence of air in the hydraulic booster or the power steering system.
^ You may notice a moan or low frequency hum (usually accompanied by a vibration in the brake pedal or steering column) during parking or other low speed maneuvers. The moan may be caused by insufficient power steering fluid, or air in the fluid. Holding the steering wheel turned as far as possible in 1 direction holds the power steering pump at relief pressure. Holding the pump at relief pressure for more than 5 seconds causes air to enter the system. Verify the cause of the noise using the following procedure:
1. Test the fluid level. Fill the fluid reservoir as needed.
2. Turn OFF the engine.
3. Allow the vehicle to sit for 1 hour. Any air in the system will escape.
4. Verify that the moan is no longer present. If the moan persists, refer to Power Steering System Test Procedure in Power Steering System.

^ You may hear a high-speed fluid noise when fully applying the brake pedal. The noise is normal.
^ You may notice a slight hiss while the accumulator pressure is in use. The hiss is hydraulic fluid escaping through the accumulator valve. The noise is normal.
^ If the accumulator is empty when the engine is started, you may hear a hissing noise during the first brake application or steering maneuver. The noise is fluid rushing through the accumulator charging orifice. The noise is normal. The noise should be heard only once after the accumulator is emptied.
If the noise continues, even though no apparent accumulator pressure assist occurred, the noise may indicate that the accumulator is not holding pressure. Inspect the accumulator. Refer to Accumulator Leak-Down Test.