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.