1. The power steering feels heavy or lacks assistance

Symptoms:
Heavy steering, with brief loss of hydraulic power assistance

Causes of fault: 

① Loose V-belt on the oil pump 

② Oil level in the reservoir too low 

③ Insufficient oil pump pressure 

④ Pressure control valve sticking 

⑤ Excessive external leakage 

⑥ Excessive internal leakage 

⑦ Steering shaft bushing too tight 

⑧ Front suspension deformation 

⑨ Air in the hydraulic system

Troubleshooting: 

① Check the condition of the power steering pump drive assembly. Press down on the power steering pump drive belt by hand; if it compresses excessively, this indicates that the drive belt is too tight and needs adjusting. Start the engine and allow it to run at idle speed, then suddenly increase the engine speed to check whether the power steering pump drive belt slips. If slippage occurs, this indicates that the drive belt is too loose or excessively worn, and it should be adjusted or replaced.

② Check the level of the steering fluid in the reservoir. If the level is below the lower mark or the ‘MIN’ mark, this indicates that the steering fluid is low and should be topped up to the specified level.

③ Check the filter in the power steering fluid reservoir. Remove the filter and inspect the condition of the filter screen. If the filter screen is excessively dirty, this indicates that the filter is blocked and should be cleaned; if the filter screen is torn, it should be replaced.

④ Check for air in the system. First, start the engine and allow it to run at idle speed, then turn the steering wheel back and forth several times and observe the condition of the steering fluid. If the steering fluid is foamy or cloudy, this indicates that air has entered the steering system and must be bled out; check whether the steering oil pump’s inlet hose is cracked; if so, replace it; Check whether any of the pipe joints are loose; if so, tighten them; check whether the seal ring on the steering oil pump shaft is damaged; if there is an oil leak, replace it with a new part.

⑤ Check the oil pressure in the steering system. Connect a pressure gauge between the steering oil pump and the power steering unit, run the engine at idle, and close the pressure gauge valve. If the pressure does not reach the specified value within 10 seconds, this indicates insufficient pressure from the steering oil pump, which should be dismantled, inspected and repaired. Turn the steering wheel to its left or right limit position, open the pressure gauge valve; if the pressure does not reach the specified value, this indicates a fault with the power steering unit or that the valves are incorrectly adjusted, and it should be dismantled, inspected and adjusted.

2. The power steering system is making a noise

Symptoms:
A noise is heard coming from the power steering pump when the car is turned

Causes of failure:   

① Loose V-belt on the oil pump 

② Damaged oil pump bearings 

③ Damage to the pressure plate or rotor 

④ Excessive wear on the oil pump ring 

⑤ Insufficient oil in the reservoir 

⑥ Air in the hydraulic system or loose pressure hose connections 

⑦ Incorrect assembly of the oil pump 

⑧ Faulty relief valve

Troubleshooting: 

① Check the level of the steering fluid in the reservoir. If the level is below the lower mark or the ‘MIN’ mark, this indicates that the steering fluid level is too low; top up to the specified level. If the steering fluid is being consumed too quickly, this indicates a serious leak, which should be investigated and rectified.

② Check the condition of the power steering pump drive assembly. Press down on the power steering pump drive belt by hand; if it deflects too much, this indicates that the drive belt is too loose and should be adjusted.

③ Check for air in the power steering fluid. Open the reservoir cap, start the engine and let it run at idle speed, then turn the steering wheel back and forth several times to check for bubbles in the power steering fluid. If bubbles are present, this indicates that air has entered the power steering fluid and must be bled out.

④ Check whether the filter screen on the oil reservoir is blocked and whether the oil piping is correctly routed. Remove the filter screen from the oil reservoir; if it is excessively dirty, this indicates that the oil is not circulating properly and it should be cleaned; if the oil piping is kinked or dented, it should be replaced.

⑤ If all the above test results are correct, the steering oil pump should be dismantled and inspected to check for scratches on the vanes and the pump housing; replace the relevant parts as necessary based on the findings of the inspection.

3. The steering feels different on the left and right

Symptoms:
Whilst the vehicle is in motion, the steering effort required to turn left and right is not equal.

Causes of fault: 

① The spool (or slide valve) of the steering control valve is out of the centre position, or, although it is in the centre position, the clearance between it and the shoulder of the valve body is inconsistent;

② Debris inside the control valve is causing blockages, resulting in different levels of resistance when turning it to the left and right;

③ Air has entered one of the oil chambers of a power cylinder in the hydraulic system;

④ Oil leakage

Troubleshooting: 

This fault is usually caused by contaminated oil; replace the oil with fresh oil in accordance with the specifications before carrying out any checks.

① If the fault persists despite the oil being of good quality or having been replaced with fresh oil, the hydraulic system should be bled and checked for oil leaks. Should a leak be found in the hydraulic system, the components at the leak point should be replaced; 
 ② If the fault still cannot be rectified, it may be caused by poor centring of the control valve. Faults in spool-type steering control valves can be rectified externally to the power steering unit by adjusting the position of the valve body. If the fault persists after adjusting the spool position, the spool should be dismantled and inspected to measure its dimensions; if there is significant deviation, the spool should be replaced. For rotary-type steering control valves, the fault must be rectified by dismantling and inspecting the valve.

The steering systems fitted to motor vehicles can broadly be categorised into three types: (1) Mechanical hydraulic power steering systems; (2) Electro-hydraulic power steering systems; (3) Electric power steering systems.

 I.Electric Power Steering System (EPS)

1. The full English name is Electronic Power Steering, abbreviated as EPS. It utilises power generated by an electric motor to assist the driver with power steering. Although the structural components differ across vehicles, the basic composition of EPS is largely similar. It typically comprises a torque (steering) sensor, an electronic control unit, an electric motor, a reduction gear, a mechanical steering gear, and a battery power source.

2. Primary operating principle: During steering manoeuvres, the torque (steering) sensor detects the steering wheel's applied torque and intended direction of rotation. These signals are transmitted via the data bus to the electronic control unit. Based on input data such as applied torque and intended steering angle, the ECU issues operational commands to the motor controller. The motor then generates an appropriate counter-torque output to assist steering effort. When no steering input is applied, the system remains inactive in standby mode, awaiting activation. Due to the operational characteristics of electric power steering, drivers typically perceive enhanced steering feel and greater stability at high speeds, commonly described as ‘steering that doesn't feel loose or vague’. Furthermore, its non-operational state during non-steering periods contributes to energy savings. This type of power steering system is commonly employed in premium saloon vehicles.

Compared to mechanical hydraulic power steering systems, electric power steering requires only electricity and eliminates numerous components. It dispenses with the hydraulic system's oil pump, oil lines, pressure/flow control valves, reservoir, and other elements. This results in fewer parts, easier layout, and reduced weight.

Moreover, it eliminates parasitic losses and fluid leakage losses. Consequently, electric power steering achieves approximately 80% energy savings under various driving conditions, enhancing the vehicle's operational performance. Consequently, it has seen rapid adoption in recent years and represents the future trajectory for power steering systems.

Some vehicles marketed as featuring electric power steering do not employ a genuinely pure electric system; they still require a hydraulic system, albeit one supplied by an electric motor. In traditional hydraulic power steering systems, the oil pump is driven by the engine.

To ensure light steering effort during stationary or low-speed manoeuvres, the pump's displacement is determined by the flow rate at engine idle speed. However, as vehicles spend most of their time travelling at speeds above idle and in straight-line motion, the majority of the oil pump's output must be returned to the reservoir via control valves, resulting in significant parasitic losses.

To mitigate these losses, an electric motor-driven oil pump is employed. During straight-line driving, the motor operates at low speed, while during steering manoeuvres it runs at high speed. By regulating the motor's rotational speed, the oil pump's flow rate and pressure are adjusted, thereby reducing parasitic losses.

II. Mechanical Hydraulic Power Steering Systems

1. Mechanical hydraulic power steering systems typically comprise a hydraulic pump, oil lines, pressure-flow control valve body, V-belt drive, reservoir, and other components.

2. This system operates continuously regardless of steering input. During sharp turns at low speeds, the hydraulic pump must deliver greater power to provide substantial assistance, thereby wasting resources to some extent. Consider this: when driving such vehicles, particularly during low-speed turns, the steering feels heavy and the engine labours noticeably. Moreover, the high pressure generated by the hydraulic pump can readily damage the power steering system. Furthermore, mechanical hydraulic power steering systems comprise hydraulic pumps, piping, and cylinders. To maintain pressure, the system remains active regardless of steering assistance requirements, resulting in higher energy consumption – another factor contributing to resource expenditure. Such systems are commonly found in economy-class saloon cars.

 III. Electronically Controlled Hydraulic Power Steering System

1. Primary Components: Reservoir tank, power steering control unit, electric pump, steering gear, power steering sensor, etc., wherein the power steering control unit and electric pump form an integrated assembly.

2. Operating Principle: The electronic hydraulic power steering system overcomes the shortcomings of conventional hydraulic power steering systems. Its hydraulic pump is no longer directly driven by the engine belt but instead utilises an electric pump. All operational states are determined by the electronic control unit, which calculates the optimal conditions based on signals such as vehicle speed and steering angle. Simply put, during low-speed, high-angle turns, the ECU drives the electric hydraulic pump at high speed to deliver greater power, reducing steering effort for the driver. At high speeds, the hydraulic control unit operates the electric pump at lower speeds, conserving engine power without compromising high-speed steering responsiveness.

SAE J188 High-Capacity Intumescent Power Steering Hose

Application: For vehicles equipped with power steering systems, used to transmit pressure within the power steering unit.

Operating temperature: -40°C to 121°C, with a peak temperature of up to 135°C.

Standard inner diameter: 3/8”. The primary material is CSM, which offers excellent resistance to ozone, ageing, chemical corrosion, high and low temperatures, oil, abrasion, and electrical insulation.

SAE J189 Low-Pressure Power Steering Return Hose

Application: For vehicles equipped with power steering systems; used to transmit pressure within the power steering unit.

Operating temperature: -40°C to 121°C, with a maximum instantaneous temperature of 135°C.

Common inner diameter: 3/8”.

Single-layer polyester filament braiding.

SAE J190 steel-braided power steering hose

Operating temperature: -40°C to 120°C.

Inner layer: NBR

Reinforcement: single or double layer of copper-plated steel braiding.

Outer layer: CR

Common inner diameters: 5/16”, 3/8”, 1/2”, 5/8”.

Typically used with crimp fittings.

Steel-braided high-temperature power steering hose

Operating temperature: -40°C to 150°C.

Reinforcement layer: Two layers of polyester filament braiding. The main material is ACM, which offers excellent heat resistance, ageing resistance, oil resistance, ozone resistance and UV resistance. Its mechanical and processing properties are superior to those of fluorocarbon rubber and silicone rubber. Its heat resistance, ageing resistance and oil resistance are superior to those of nitrile rubber.

• Contact Us for Vehicle-Specific AC Pipes: natasha@nafurancar.com

I.How it works

Core function: to convert the rotation of the steering wheel into wheel movement, thereby steering the vehicle.

1. Mechanical steering (non-power-assisted).

Steering wheel → steering column → steering gear (rack and pinion/recirculating ball) → steering linkage → steering knuckle → wheel deflection; driven entirely by human effort.

2. Hydraulic power steering (HPS).

The mechanical structure is supplemented by a hydraulic pump, hydraulic hoses and a power steering cylinder. The engine drives the hydraulic pump to generate pressure, which assists the steering mechanism, making steering lighter.

3. Electric Power Steering (EPS).

Power assistance is provided directly by an electric motor, a torque sensor and a controller. It offers quick response, improved fuel economy and a simple design, and is currently the mainstream technology.

II. Common faults and solutions

1. Heavy steering; steering requires considerable effort.

Possible causes:

(1) Tyres are under-inflated.

(2) Hydraulic power steering system is low on fluid, has a leak, or the power steering pump is worn.

(3) Fault in the electric power steering motor or sensor.

(4) The ball joint on the steering tie rod or the plain bearing is seized.

Solution:

(1) Inflate the tyres to the recommended pressure.

(2) Check the power steering fluid; top up or replace it, and repair any leaks.

(3) Use a diagnostic scanner to read the EPS fault codes, and repair the sensors or motor.

(4) Lubricate or replace the ball joints and bearings.

2. Steering wheel pull (vehicle pulls to the left or right when driving in a straight line).

Possible causes:

(1) Uneven tyre pressure between the left and right tyres.

(2) Incorrect wheel alignment.

(3) Brake calipers sticking, causing uneven braking force between the left and right sides.

(4) Uneven lengths of the steering tie rods.

Solutions:

(1) Ensure all tyres are at the correct pressure.

(2) Have a four-wheel alignment carried out.

(3) Check the braking system.

(4) Adjust the steering linkage.

3. Steering noise (clunking or squeaking when turning the wheel).

Possible causes:

(1) Ageing of the steering ball joints or lower control arm rubber bushings.

(2) Wear on the plain bearings or top bushings.

(3) Stiff steering column universal joint.

(4) Noise caused by low fluid level in the power steering pump.

Solutions:

(1) Replace the ball joints and rubber bushings.

(2) Replace the shock absorber top bushings or plain bearings.

(3) Lubricate or replace the universal joints.

(4) Top up or replace the power steering fluid.

4. Steering wheel vibration and instability at high speeds.

Possible causes:

(1) Incorrect tyre balancing.

(2) Excessive play in the steering system.

(3) Warped wheel rims or bulging tyres.

Solutions:

(1) Have the tyres balanced.

(2) Check and tighten all components of the steering mechanism.

(3) Replace warped wheel rims or bulging tyres.

5. The steering lacks power and feels alternately light and heavy.

Possible causes:

(1) Blown EPS fuse or wiring fault.

(2) Power steering pump belt slipping or broken (hydraulic system).

(3) Power steering fluid too dirty or clogged.

Solutions:

(1) Check the fuse and wiring harness; repair the EPS module.

(2) Adjust or replace the belt.

(3) Replace the power steering fluid and flush the system.

6. The steering wheel is difficult to centre or does not return to its original position automatically.

Possible causes:

(1) Incorrect rearward or inward camber of the kingpins during wheel alignment.

(2) Sticking in the steering mechanism.

(3) Power steering system fault.

Remedies:
Perform wheel alignment, lubricate or replace steering components, and service the power steering system.

III. Recommendations for Routine Maintenance

1. Avoid turning the steering wheel fully to either side whilst stationary to reduce the load on the power steering system.

2. For vehicles with hydraulic power steering, change the power steering fluid regularly.

3. Have any unusual noises, pulling to one side or heavy steering checked as soon as possible to prevent minor faults from escalating.

4. Have a four-wheel alignment carried out promptly following an accident or any impact to the chassis.