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Published:2026.04.28　Updated:2026.04.28

Hydraulic System Troubleshooting: Common Problems, Causes, and Solutions

When a hydraulic system problem develops in construction equipment, it can seriously disrupt jobsite operations by causing slow movement, lack of power, or sudden stoppages.
Because hydraulic trouble often has multiple possible causes, it is not always easy to know where to begin the inspection.

This article breaks down the symptoms commonly seen in hydraulic system failures and their underlying causes.
It also explains practical on-site troubleshooting steps, corrective actions for major components, and key points for choosing parts that help prevent repeat problems after repairs.
Use it as a reference for daily inspections and repair decisions.

Common Symptoms That Indicate Hydraulic System Trouble

When construction equipment in operation begins to malfunction, it is essential to detect the warning signs as early as possible.

The four main symptoms that typically appear when the hydraulic system is not functioning properly are as follows.

Slow operation or lack of power
Unusual noises
Rising hydraulic fluid temperature
Oil leaks

Recognizing these changes makes it easier to pinpoint the cause of the problem.

Slow Operation and Insufficient Force

Insufficient force and slow operation in hydraulic equipment do not necessarily have the same cause.
Insufficient pressure reduces digging and lifting force, while insufficient flow slows the movement of the boom, arm, and other components.

If all functions are affected, check for the following:

A low hydraulic oil level
Clogged filters
Internal pump leakage
Incorrect relief valve settings

If only one function operates slowly, the associated control valve, cylinder, or motor may be at fault.

Do not keep operating the machine despite these symptoms. Record which functions are affected and arrange for an inspection.

Unusual Noises

The type of noise alone is not enough to determine whether there is an internal fault in the hydraulic pump.

Aeration occurs when outside air enters the hydraulic oil through pipe connections or other points.

Cavitation, on the other hand, occurs when a drop in suction pressure causes bubbles to form in the hydraulic oil.

Internal pump wear and coupling misalignment can also cause unusual noises.

During inspection, do not rely on sound descriptions alone. Record which operation produced the noise and the engine speed at the time.

Also check the hydraulic oil level, look for a milky appearance, and inspect the condition of the suction piping.

Stop operating the machine if there is severe vibration or metallic noise.

Rising Hydraulic Oil Temperature

An increase in hydraulic oil temperature can result from problems in the hydraulic circuit as well as in the cooling system. Common causes include:

A clogged oil cooler
Internal leakage in the circuit
Continuous relief valve operation
Incorrect hydraulic oil viscosity

The appropriate operating temperature and warning threshold vary by machine model and hydraulic oil, so use the values specified in the operator’s manual as your reference.

Do not assess the temperature by touching the machine’s surface. Check the machine’s display for warnings or use the oil temperature gauge.

If the temperature remains above the specified limit, stop operating the machine and arrange for the cooling system and hydraulic circuit to be inspected.

Oil Leaks

Hydraulic oil leakage can be external, where oil escapes from the machine, or internal, where oil passes through clearances inside valves or cylinders. The main points to inspect for external leaks are:

Hydraulic hoses
Pipe fittings
Pump shaft seals
Areas around cylinder rods

Internal leakage is difficult to detect visually. Symptoms such as insufficient force or unintended lowering of the work equipment may indicate internal leakage, which is diagnosed by measuring pressure and leakage rates.

High-pressure hydraulic oil can penetrate the skin, so never use your hands to locate a leak.

If you discover a leak, stop the machine, take appropriate safety precautions, and consult a specialist.

No Movement or Erratic Operation

The likely causes differ depending on whether the hydraulic equipment does not move at all or operates intermittently.
If none of the machine’s functions operate, check the following:

Engine and pump operation
Insufficient pilot pressure
Faults in the solenoid valves or wiring
Whether the safety lock mechanism is engaged

If the equipment starts and stops intermittently, possible causes include poor electrical connections, loose connectors, or malfunctioning solenoid valves.

A low hydraulic oil level or clogged filters may also cause an inconsistent oil supply.

Record any warning messages and the operations during which symptoms occur. When isolating the cause, it is important to consider the engine and electrical system as well as the hydraulic components.
To prevent unintended movement, stop the machine in a safe location and have a specialist carry out any diagnostics beyond the checks covered in the operator’s manual.

Main Causes of Hydraulic System Trouble

Behind the visible symptoms are underlying issues that reduce the performance of the system.

The four most common causes of hydraulic system trouble are as follows.

Contaminated hydraulic fluid
Air entering the system
Excessive hydraulic fluid temperature
Abnormal pressure

When these factors occur individually or in combination, the machine can no longer operate properly.

Hydraulic Oil Contamination

Dirt, metal particles, and water in hydraulic oil can damage the sliding surfaces in hydraulic pumps and valves, causing wear and operating problems.

Dirt can enter during filling or through deteriorated seals, while metal particles are generated by wear on internal components.

Water can also be introduced during filling or accumulate through condensation inside the tank.

As contamination worsens, valves may stick and internal leakage may develop, potentially causing pressure to drop.

Even if the hydraulic oil looks clean, fine contaminants and water cannot be reliably detected by visual inspection alone.

Take hydraulic oil samples as needed and have them analyzed for contamination levels, water content, and wear metals.

Air Entering the System

Air mixed into the hydraulic fluid, creating bubbles, is another major cause of serious damage.
It can occur when air is drawn in through loose pipe connections or when the fluid level in the tank is too low.

When these bubbles are compressed under high pressure inside the pump and then collapse, they create shock waves strong enough to erode metal surfaces.
This causes severe vibration and noise and can drastically reduce system efficiency.
Checking the suction hose for cracks and making sure the hydraulic fluid is always at the proper level are important steps in avoiding this kind of trouble.

Excessive Hydraulic Fluid Temperature

Hydraulic fluid temperature rising beyond the proper range is another major factor that can stop the system from functioning properly.
It may be caused by insufficient cooling capacity or a malfunction such as a relief valve remaining open.

Excessive heat accelerates fluid deterioration and significantly reduces its lubricating performance.
As friction between metal parts increases, packings may melt or harden, leading to even more leakage.
During hot weather, especially in summer, hydraulic fluid temperature rises more easily, so debris should be removed from the radiator or cooler and good airflow should be maintained.

Abnormal Hydraulic Pressure

Insufficient pressure and excessive pressure have different potential causes and effects on the machine.

If pressure fails to build, possible causes include reduced pump output, incorrect relief valve settings, or internal leakage within the circuit.

If insufficient force affects only one function, the associated control valve and actuator also need to be checked.

Excessive pressure, on the other hand, may indicate that the relief valve setting is too high, a valve is stuck, or the pump control system is malfunctioning.

Excessive pressure places stress on hoses and cylinders, so do not continue operating the machine.

Pressure measurements and adjustments should be carried out using appropriate gauges by maintenance personnel who can verify the specified values and test conditions for the particular machine model.

Steps for Identifying the Cause of Hydraulic System Trouble

When a problem occurs on site, the key to resolving it quickly is not to start dismantling the machine at random, but to observe the situation in a logical sequence.

To narrow down the cause, follow these three steps.

Secure safety and perform a visual inspection
Check sound, temperature, and pressure
Identify the faulty component

A logical inspection process helps prevent oversight and leads to a more accurate diagnosis.

Secure Safety and Perform a Visual Inspection

Before starting any troubleshooting work, stop the engine, eliminate the risk of high-pressure oil discharge, and make sure the area is safe.
Then gather as much information as possible from the machine’s outward appearance.

Check the hydraulic fluid tank gauge to confirm that the level is within the specified range, and inspect the hoses for crushing or twisting.
It is also important to look underneath the machine for any signs of oil leakage.
By identifying visible abnormalities first, you can determine where to focus the next stage of inspection and narrow down the cause more efficiently.

Check for Unusual Noises and Monitor Temperature and Pressure

After the visual inspection, record the conditions under which unusual noises occur and the instrument readings. The main items to check are:

Pressure under no-load and loaded conditions
Changes in hydraulic oil temperature
Operations that produce unusual noises
Operating time before symptoms appear

Do not assess readings in isolation. Compare them with the model-specific values listed in the operator’s manual and records from normal operation. Likewise, do not determine the cause of an unusual noise from the sound alone.

Also check the engine speed and load conditions at the time it occurs.

Check the hydraulic oil temperature using the machine’s display or a measuring instrument. Never touch hot components directly.

Measuring pressure or changing pressure settings requires specialist knowledge and appropriate gauges.

If you are unsure how to proceed, have maintenance personnel or a specialist service provider carry out the work.

Identify the Faulty Component

Once the likely cause becomes clearer, the final step is to diagnose which specific component has failed.
The most reliable approach is to follow the hydraulic system in order, from the power source to the actuator.

Start by checking the pump’s discharge flow, then inspect the movement of the control valve, and finally check the cylinder for internal leakage.
In some cases, more than one component may have failed at the same time, so even after one problem is found, the inspection should continue until the entire system has been checked.

Component-by-Component Troubleshooting and Corrective Procedures

Once the cause has been identified, the next step is to apply the appropriate corrective action based on the affected component.

The following three components are the ones most commonly handled on site.

Hydraulic pump
Hydraulic valve
Hydraulic cylinder

Understanding the diagnostic criteria and maintenance approach for each type of component will improve the quality of the repair.

Hydraulic Pump

Before disassembling the hydraulic pump, check the following:

Hydraulic oil level
Suction filter blockage
Cracks or loose connections in the suction piping
Condition of drive components, such as the coupling
Pump discharge pressure and flow

An incorrect hydraulic oil level or suction-side problems can reduce performance even if the pump itself is functioning properly. Take measurements under consistent oil temperature, engine speed, and load conditions, and compare the readings with the specifications for the machine model.

If pressure or flow remains insufficient after these checks, internal damage may be the cause.
Have a specialist with performance testing facilities disassemble and inspect the pump, then determine whether to overhaul or replace it based on the extent of damage and the cost.

Hydraulic Valves

Hydraulic valve malfunctions can result from sticking caused by contaminants or from electrical faults.

Contaminants in the hydraulic oil can enter the area around the spool and prevent it from moving freely.

Faults in the solenoid valve or wiring, on the other hand, can prevent the valve from receiving the correct control signals.

During diagnosis, identify which functions are affected and measure electrical signals and pilot pressure to isolate the cause.

Leave the removal and disassembly of valves in high-pressure circuits to specialists.

A specialist will inspect the internal components and determine whether removing contaminants or replacing seals is sufficient.

If the spool or valve body is severely worn, the valve must be replaced.

Hydraulic Cylinders

Hydraulic cylinder leakage can be external, with oil escaping around the rod, or internal, with oil passing through clearances inside the cylinder. For external leaks, identify the source.
Internal leakage is diagnosed by measuring holding capacity and pressure.

However, unintended lowering of the boom or other work equipment can also result from valve faults, so symptoms alone are not enough to confirm a cylinder fault.

Typical repair work includes:

Replacing the seal kit
Repairing the rod surface
Inspecting the inner surface of the cylinder tube
Replacing the cylinder assembly

Even if the rod is scratched, regrinding or replating may be an option, depending on the depth of the damage and the extent of any bending.
If the damage is extensive, consider replacing the cylinder assembly.

Choosing the Right Parts and Managing Lifecycle Cost to Prevent Problems After Repair

When replacing parts, choosing solely on upfront price can lead to repeat failures, so decisions should be made with a long-term perspective.
Used parts, third-party products, counterfeit parts, and imitation goods may reduce initial cost, but because their performance is not guaranteed, they also carry the risk of another shutdown.

By contrast, genuine manufacturer parts offer assured quality and restore the machine’s intended performance.
Even when non-genuine parts look similar, they often do not meet the original design tolerances or material standards, which can damage surrounding components and lead to unexpected downtime.
Choose parts with the machine’s operating frequency and total lifecycle cost in mind.

Summary: Hydraulic System Trouble Is Best Resolved Through Early Detection and Proper Maintenance

Stable operation of construction equipment depends on choosing quality-assured parts.
If you need to confirm whether the hydraulic pump or motor on your machine is genuine and arrange the correct replacement parts, make use of “Kawasaki Hydraulic Finder.”

By simply entering the serial number shown on the nameplate, you can identify genuine parts and confirm accurate information, making it easier to arrange parts through an official dealer.
If the number cannot be read, you can also scan it with the camera function or note it down and contact an authorized dealer directly.
Use this service as part of your daily maintenance to help maintain a safe and efficient working environment.

Reviewed by

Ryoji Irie

Manager
After-Sales Promotion Office, Marketing & Sales Group, Precision Machinery & Robot Company, Kawasaki Heavy Industries, Ltd.

《Career History》

After joining Kawasaki Heavy Industries, I spent ten years developing the new K7V pump series as a design engineer, followed by five years at KPM (UK) as an application engineer supporting European OEMs and distributors. I am currently responsible for promoting the after-sales business globally.