1. Power steering feels heavy or lacks assistance

Fault Symptom:

The steering becomes heavy, with a brief loss of hydraulic assistance.

Cause of malfunction:

① Oil pump V-belt slack

② Oil reservoir level too low

③ Insufficient oil pump pressure

④ Pressure control sticking

⑤ Excessive external leakage

⑥ Excessive internal leakage

⑦ Steering shaft bushing too tight

⑧ Front suspension deformation

⑨ Air present in hydraulic system

Exclusion method:

① Inspect the condition of the steering pump drive assembly. Manually depress the drive belt of the steering pump; excessive deflection indicates the belt is excessively tight and requires adjustment. Start the engine and allow it to idle. Abruptly increase engine speed to check for belt slippage. Any slippage indicates the drive belt is either too loose or excessively worn, necessitating adjustment or replacement.

② Check the fluid level in the reservoir. Should the level be below the lower mark or ‘MIN’ line, insufficient fluid is present and should be topped up to the specified level.

③ Inspect the reservoir's filter. Remove the filter and examine the screen. If excessively dirty, the filter is clogged and requires cleaning; if cracked, it must be replaced.

④ Check for air ingress in the system. First, start the engine and allow it to idle. Then turn the steering wheel several times in both directions. Observe the condition of the steering fluid. If foam is present or the fluid appears cloudy, this indicates air has entered the steering system and must be purged. Inspect the steering pump's inlet hose for cracks. If cracked, replace it. Inspect all pipe connections for looseness; tighten any loose fittings. Examine the seal ring on the steering pump shaft for damage; replace with a new part if oil leakage is detected.

⑤ Check the steering system's oil pressure. Connect a pressure gauge between the steering pump and power steering unit. With the engine idling, close the gauge valve. If the pressure fails to reach the specified value within 10 seconds, this indicates insufficient pressure from the steering pump. The pump should be disassembled for inspection and repair. Turn the steering wheel to its left or right limit position, then open the gauge valve. If the pressure fails to reach the required value, this indicates a fault with the power steering unit or improper valve adjustment. The unit should be disassembled for inspection and adjustment.

2. Power steering system is making noise

Fault Symptom:

Noise emanating from the steering pump during vehicle steering manoeuvres

Causes of Fault:

① Loose V-belt on the pump
② Damaged pump bearings
③ Faulty pressure plate or rotor
④ Excessive wear on pump rings
⑤ Insufficient reservoir fluid
⑥ Air ingress in hydraulic system or loose pressure hose connections
⑦ Improper pump assembly
⑧ Malfunctioning relief valve

Troubleshooting Procedure:

① Inspect the steering fluid level within the reservoir. Should the level fall below the lower mark or ‘MIN’ line, this indicates insufficient fluid and necessitates topping up to the specified position. Excessive fluid consumption suggests a significant leak, requiring investigation and rectification.

② Examine the steering pump drive assembly. Manually depress the steering pump drive belt. Excessive deflection indicates a loose belt, requiring adjustment.

③ Verify the presence of air in the steering hydraulic system. Open the reservoir cap, start the engine at idle speed, and turn the steering wheel several times. Observe for bubbles in the fluid. If bubbles are present, air has entered the system and must be purged.

④ Verify the reservoir filter screen is unobstructed and the hydraulic lines are correctly routed. Remove the reservoir filter screen; if excessively soiled, indicating poor fluid circulation, clean it. Replace any kinked or dented hydraulic lines.

⑤ Should all preceding checks prove satisfactory, disassemble and inspect the steering pump. Examine the vanes for scratches and the pump housing for damage. Replace any affected components based on the inspection findings.

3. Uneven steering effort when turning left or right

Fault Symptom:

During vehicle operation, unequal steering effort is required when turning left and right.

Causes of Fault:

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

② Contaminants within the control valve cause obstruction, resulting in differing rotational resistance when turning left or right;

③ Air ingress into one oil chamber of the power cylinder within the hydraulic system;

④ Oil leakage in the circuit.

Troubleshooting Methods:

This fault is often caused by contaminated hydraulic fluid. Replace the fluid with fresh oil as specified before further inspection.

① If the oil quality is satisfactory or the fault persists after replacement, bleed the hydraulic system and inspect for oil leaks. Replace components at any leakage points.

② Should the fault persist, it may stem from improper centring of the control valve. For spool-type steering control valves, rectification can be performed externally on the power steering unit by adjusting the spool position within the valve body. If no improvement occurs after spool repositioning, disassemble and inspect the spool, measuring its dimensions. Replace the spool if significant deviations are found. For rotary-type steering control valves, fault diagnosis necessitates complete disassembly and inspection.

When reviewing the specification sheet, have you noticed an entry labelled ‘Power Steering Type’? Common options in this section include mechanical hydraulic power steering, electronic hydraulic power steering, and electric power steering. What exactly does ‘Power Steering Type’ refer to? What do these three variants represent? What are the differences and respective advantages and disadvantages of each method?

We've all experienced it firsthand: when the engine isn't running, even with all your strength, it's incredibly difficult to turn the steering wheel. Just imagine – can you really expect to effortlessly manoeuvre something weighing nearly two tonnes? To tackle this issue, a system known as power steering was developed. As the name suggests, its purpose is to assist you in turning the wheel. Currently, the market primarily offers three types of power steering: mechanical hydraulic power steering, electronic hydraulic power steering, and electronic power steering.

1.Mechanical hydraulic power steering

Mechanical hydraulic power steering systems typically comprise components such as a hydraulic pump, oil lines, pressure and flow control valve bodies, drive belts, and reservoir tanks. The operating principle involves the hydraulic pump generating oil pressure to actuate a piston, thereby producing an auxiliary force that drives the steering linkage to assist wheel turning. Vehicles equipped with this system often exhibit heavier steering feel and increased engine load during low-speed, wide-radius turns. Due to the high pressure generated by the hydraulic pump, the power steering system is also more susceptible to damage. Mechanical hydraulic power steering systems are commonly employed in most economy saloon cars.

2.Electronic Hydraulic Power Steering

Primarily comprising a reservoir tank, power steering control unit, electric pump, steering gear, and power steering sensor, the electronic hydraulic power steering system employs an electrically driven electric pump, wherein the power steering control unit and electric pump form an integrated assembly. This system enables smoother cornering and driving by calculating the optimal steering assistance based on signals such as vehicle speed and steering angle, as determined by the electronic control unit. The electronic hydraulic power steering system is currently the most widely adopted power steering system.

Generally comprising a steering sensor, electronic control unit, electric motor, reduction gear, mechanical steering gear, and power supply, the specific configuration may vary. The absence of hydraulic components such as the hydraulic pump, hydraulic lines, and steering column valve body results in a simpler structure. Under the control of the electronic control unit, the vehicle can readily achieve variable assistance functionality. This means greater assistance energy and lighter steering at lower speeds, while reduced assistance energy and heavier steering are provided at higher speeds. When no steering input is required, the system remains inactive, entering a dormant state awaiting activation. Such power steering systems are commonly found in premium saloon cars, and an increasing number of vehicles are now adopting this form of steering assistance.

Power steering fluid, being subjected to continuous extreme pressure and high-temperature conditions, will deteriorate and become contaminated over time, losing its lubricating properties. This leads to the formation of deposits such as varnish, causing steering difficulties and steering wheel vibration. The power steering system is crucial to our driving safety.

How often should power steering fluid be changed? While vehicle manufacturers do not strictly stipulate a replacement interval for power steering fluid, it is advisable to replace it every 40,000 to 50,000 kilometres or within 2 to 3 years to prevent contamination or degradation that could lead to further issues. Should inspection of the power steering system reveal the fluid level below the minimum mark, a noticeable thinning of the fluid, or a darkening of its colour, replacement should be carried out immediately.

Finally, a word of caution to many motorists who habitually substitute gearbox oil for steering fluid: this practice is not recommended. The two fluids differ in viscosity, molecular structure and function, and may damage the steering mechanism. While the effects may not be immediately apparent, the internal rubber seals within the steering unit will deteriorate, leading to persistent oil leakage. The steering system is crucial for driving safety, reducing the effort required to turn the wheel and ensuring a smoother driving experience. Therefore, regular maintenance and inspection are absolutely essential!

Different types of power steering systems require distinct maintenance approaches. For mechanical hydraulic systems, routine checks must prioritise ensuring the power steering reservoir remains adequately filled with steering fluid. Additionally, avoid holding the steering wheel at full lock for extended periods. Regularly monitor whether steering feels excessively heavy or produces unusual noises. Should such symptoms arise, promptly inspect components such as the oil pump V-belt and internal pressure levels. For electro-hydraulic systems, routine checks on power steering fluid levels remain crucial; immediate investigation is required whenever the warning light illuminates. Regarding electric power steering systems, despite their relatively simple construction, maintenance demands more than visual inspection. Should steering become unresponsive or exhibit heavy operation, diagnostic instruments become essential for accurate measurement.