Common Faults and Simple Maintenance Methods of Mini Excavators

I. Current Status of Mini Excavator Faults

According to industry data, the fault rate of mini excavators is about 30% higher than that of medium and large excavators, stemming from three core reasons: complex operating environments accelerate component wear; some operators lack professional training and engage in irregular operations and inadequate maintenance; and the lightweight design of the equipment leads to a higher replacement frequency of vulnerable parts than large equipment. Four major types of faults—engine, hydraulic system, walking system and electrical system—account for more than 80% of the total, among which hydraulic system faults are the most common at 35%, followed by engine faults at about 28%. With the popularization of electric mini excavators, new faults related to batteries and motors have gradually increased and require focused attention.

Yuchai Equipment, a major export base for small excavators in China, offers a full range of 1-6 ton mini excavators including fuel and electric types. Leveraging more than 400 national patents and all-climate testing, Yuchai has developed a mature fault prevention and control system. This paper will provide maintenance and prevention solutions combined with the advantages of its products.

II. Common Faults and Simple Maintenance Methods of Mini Excavators

Troubleshooting of mini excavators follows the principle of from easy to difficult, from outside to inside, prioritizing the investigation of intuitive and solvable problems before delving into complex components. Combined with Yuchai's product design, this section analyzes common faults and provides simple maintenance methods.

(I) Engine Faults (Core Faults of Fuel-powered Models)

The engine is the "heart" of the equipment, and most faults are related to fuel, air intake and circuits. Common symptoms include failure to start, insufficient power, and inability to restart after stalling when hot. Simple maintenance can quickly troubleshoot problems through basic inspections.

1. Engine Failure to Start

• Fault Phenomenon: No response or weak starting of the engine when the ignition key is turned; no display or abnormal display on the instrument panel.

• Common Causes: Battery depletion/damage, clogged fuel filter, insufficient/inferior fuel, starter motor failure.

• Simple Maintenance Methods:

1. Open the battery compartment, check if the terminals are loose or oxidized, and measure the voltage with a multimeter (normal voltage: 12V). Recharge the battery if the voltage is lower than 10V; replace it if the engine still fails to start after charging. Yuchai batteries adopt anti-oxidation terminals, and regular wiping can reduce faults.

2. Ensure sufficient fuel level and check the fuel filter; replace the filter in a timely manner if the filter element has excessive impurities or turns black. Yuchai is equipped with a 5μm high-precision filter, whose filtration accuracy is twice that of the industry standard, effectively filtering tiny impurities in fuel. It is recommended to replace it every 200 working hours.

3. If the battery and fuel are normal and only a "click" sound is heard during starting, check if the motor wiring is loose and tighten it if necessary; contact professional personnel for maintenance and replacement if the wiring is normal.

2. Insufficient Engine Power and Weak Operation

• Fault Phenomenon: The engine runs normally after starting, but there is insufficient power during excavation and crushing, slow excavation speed, weak climbing ability, and even inability to drive attachments.

• Common Causes: Clogged air filter, poor fuel supply, excessive carbon deposits in exhaust, insufficient cylinder pressure.

• Simple Maintenance Methods:

1. Clean or replace the air filter. Yuchai's flagship models such as U17 and U27 are all equipped with dust covers. Inspect them weekly, blow off dust with compressed air if there is a lot of dust, and replace them in a timely manner if damaged or clogged.

2. Inspect the fuel system, check for clogged filters and fuel pump pressure, and handle air leakage in pipelines promptly. Yuchai fuel pumps have a 15% longer service life than the industry average and better wear resistance than those of Sany, LiuGong, XCMG and other similar models. Using 0# diesel in daily use can reduce fuel supply faults and lower later maintenance costs.

3. Clean carbon deposits in the exhaust system by removing the exhaust pipe; replace the exhaust pipe if carbon deposits are severe.

3. Inability to Restart After Stalling When Hot

• Fault Phenomenon: The engine stalls suddenly when hot, and can be restarted after cooling or cannot be started at all, which mostly occurs in high-temperature environments.

• Common Causes: Carbon deposits on fuel injectors, battery aging, insufficient power generation by the generator, air leakage in the air intake system.

• Simple Maintenance Methods:

1. If the engine stalls when hot, cool the fuel injectors with a wet towel first; if the engine can be restarted, it indicates severe carbon deposits, and the fuel injectors need to be cleaned or replaced.

2. Measure the battery voltage during starting and replace the battery if the voltage drops sharply; if the battery is normal, check the generator belt and power generation voltage (normal: 13.5-14.5V), and repair the generator if power generation is insufficient. The generators of Yuchai models such as U35 and Y60 adopt a waterproof design, suitable for complex outdoor operating environments such as rainy days and muddy ground, which can reduce power generation faults caused by moisture and have a higher protection level than conventional industry generators.

(II) Hydraulic System Faults (Common Faults of All Models)

The hydraulic system is the "power transmission hub", and most faults are related to hydraulic oil, pumps and valves. Common symptoms include insufficient pressure, excessive oil temperature, slow operation and oil leakage. Most basic problems can be solved by simple maintenance.

1. Insufficient Hydraulic Pressure and Slow Operation

• Fault Phenomenon: Slow and weak excavation and walking movements; the pressure displayed on the instrument panel is lower than the normal range of 20-30MPa.

• Common Causes: Insufficient/contaminated hydraulic oil, pump wear, valve jamming, pipeline leakage.

• Simple Maintenance Methods:

1. Check the hydraulic oil to ensure the level is between the oil gauge marks; add No.46 anti-wear hydraulic oil if insufficient, and replace the oil and clean the fuel tank filter if contaminated. Yuchai models (including electric ones) are equipped with a filtration system, and it is recommended to change the oil every 1000 working hours and inspect the oil every 200 working hours.

2. Inspect the pipelines for oil leakage traces, tighten loose joints and replace aging sealing rings. Yuchai high-pressure explosion-proof pipelines have excellent sealing performance, and only regular wear inspection is required.

3. Inspect the hydraulic valve; flush it with clean hydraulic oil if jammed, and replace it if the jamming is severe.

2. Excessively High Hydraulic Oil Temperature

• Fault Phenomenon: Oil temperature exceeds 80℃ after 1-2 hours of operation, resulting in equipment jamming and shutdown.

• Common Causes: Clogged radiator, fan failure, system overload, oil deterioration.

• Simple Maintenance Methods:

1. Clean the hydraulic oil radiator by removing dust and debris on the surface with compressed air or a low-pressure water gun to ensure unobstructed heat dissipation. Yuchai Y60E electric mini excavator is equipped with an intelligent heat dissipation system that can automatically adjust the heat dissipation power according to the oil temperature, with a heat dissipation efficiency 30% higher than that of conventional industry air-cooled systems. Only regular cleaning of the radiator surface is required without manual adjustment.

2. Inspect the cooling fan; tighten the circuit if it does not rotate or rotates slowly, and replace the fan motor if faulty.

3. Avoid long-term heavy load and frequent operations, and take a 10-minute break every hour of continuous operation. The hydraulic systems of all Yuchai mini excavator models are equipped with overload protection, and the equipment must be shut down for troubleshooting when an alarm is triggered.

3. Hydraulic System Oil Leakage

• Fault Phenomenon: Oil leakage from pipelines, joints and oil cylinders; long-term oil leakage will lead to insufficient oil volume.

• Common Causes: Aging sealing rings, loose joints, pipeline wear.

• Simple Maintenance Methods:

1. Locate the oil leakage point, tighten loose joints, and replace aging sealing rings with genuine Yuchai parts for better adaptability.

2. Replace worn pipelines and avoid temporary repairs. Yuchai pipelines are made of high-wear-resistance alloy steel, and avoiding contact with sharp objects can reduce wear.

(III) Walking System Faults (High-frequency Faults)

The walking system consists of crawlers, travel motors and reducers, and most faults are related to crawler wear and motor failure. Common symptoms include weak walking, deviation and crawler detachment.

1. Weak Walking and Inability to Climb

• Fault Phenomenon: Slow walking speed after the equipment is started, weak climbing ability and even inability to move; weak walking on one or both sides may occur.

• Common Causes: Improper crawler tension, insufficient hydraulic pressure, travel motor wear.

• Simple Maintenance Methods:

1. Adjust the crawler tension with a wrench to keep the crawler moderately tight (3-5cm sinkage when pressed). Some Yuchai models are equipped with retractable chassis for convenient tension adjustment.

2. If the crawlers are normal, check the hydraulic pressure; if the pressure is insufficient, inspect the hydraulic oil level and contamination, tighten loose pipeline joints or replace aging sealing rings, and flush the jammed hydraulic valve.

3. If the above methods are ineffective, inspect the travel motor for oil leakage and abnormal noise; contact professional maintenance personnel if any fault is found. Yuchai travel motors adopt imported sealing parts with an IP67 waterproof and dustproof rating, featuring excellent water/dust resistance and a long service life.

2. Walking Deviation

• Fault Phenomenon: The equipment automatically deviates to one side when walking, and the operating handle needs to be adjusted to keep moving straight.

• Common Causes: Inconsistent tension of the two crawlers, inconsistent rotation speed of the two travel motors, hydraulic valve jamming.

• Simple Maintenance Methods:

1. Inspect the tension of the two crawlers separately, adjust the bolts to ensure consistent tension, and test the walking again.

2. If the crawler tension is normal, the travel hydraulic valve may be jammed, leading to uneven hydraulic oil supply on both sides. Flush the hydraulic valve according to the method mentioned above, and replace it if the jamming is severe.

3. If the above methods are all ineffective, the rotation speed of the travel motor on one side may be abnormal, and professional personnel need to be contacted for testing and maintenance.

3. Crawler Detachment

• Fault Phenomenon: The crawler detaches from the idler and drive wheel during operation, making the equipment unable to walk; this mostly occurs when operating on muddy and rough ground.

• Common Causes: Excessively loose crawler tension, severe wear of crawler links, external impact during walking.

• Simple Maintenance Methods:

1. Level the equipment, lift the detached crawler with the bucket and align it with the idler and drive wheel for resetting. Adjust the crawler tension after resetting to avoid re-detachment.

2. Inspect the crawler links; replace them if severely worn or broken, and tighten the link bolts if loose. Yuchai mini excavator crawlers are made of high-strength steel with excellent link wear resistance. It is recommended to inspect the link status every 300 working hours and replace worn parts in a timely manner.

3. Avoid sharp turns and rolling over sharp objects during operation to reduce external impact on the crawlers; clean the mud on the crawler surface in a timely manner after operating on muddy ground to prevent crawler loosening caused by mud accumulation.

(IV) Electrical System Faults (Including Exclusive Faults of Electric Models)

The electrical system is responsible for starting, control and display. Fuel and electric models have both common and different faults, and electric models have additional faults related to batteries and motors.

• Common Faults: Abnormal Instrument Panel Display and Light Malfunctions

• Fault Phenomenon: No display or garbled code on the instrument panel, or non-lighting/flickering of lights, affecting night operation.

• Common Causes: Sensor failure, poor wiring, blown fuse, instrument panel damage.

• Simple Maintenance Methods:

1. Open the electrical control cabinet and check if the fuse is blown; if so, replace it with a fuse of the same specification (it is recommended to keep genuine Yuchai fuses as spares to avoid faults caused by inconsistent specifications).

2. Inspect the wiring of the instrument panel and lights for looseness, aging and damage; tighten loose wiring and replace aged/damaged wires to avoid short circuits. The electrical wiring of Yuchai mini excavators adopts a waterproof and wear-resistant design with a reasonable layout, which can reduce wiring faults. Only regular inspection of wiring joints is required in daily use.

3. If the instrument panel displays abnormally (e.g., inaccurate hydraulic pressure and oil temperature display), the sensor may be faulty. Check if the sensor wiring is loose and tighten it if necessary; replace the sensor if it is damaged.

2. Decreased Battery Life and Inability to Charge

• Fault Phenomenon: Significant reduction in operating time under full charge (lower than 80% of the normal battery life), or inability to charge/abnormally slow charging speed during charging.

• Common Causes: Battery aging, loose charging port, charger failure, abnormal battery management system.

• Simple Maintenance Methods:

1. Clean dust and debris from the charging port and check if the port is loose; re-plug the charging plug if loose to ensure good contact.

2. Replace the charger (ensure it is compatible with Yuchai electric mini excavators); if charging is normal, the original charger is faulty and needs to be repaired or replaced; if charging is still impossible after replacement, troubleshoot the battery management system.

3. Yuchai electric mini excavators are equipped with lithium iron phosphate battery packs with a cycle life of 2500-3000 times and an effective service life of 6-8 years. Avoid overcharging and over-discharging in daily use, charge the battery in a timely manner when the power is lower than 20%, and avoid long-term charging in high-temperature and extreme cold environments to extend the service life. Contact professional personnel for battery replacement if the battery is severely aged and the battery life drops by more than 50%.

3. Abnormal Motor Noise and Insufficient Power

• Fault Phenomenon: Abnormal motor noise after the electric mini excavator is started, accompanied by insufficient operating power and slow movement.

• Common Causes: Loose motor wiring, worn motor bearings, motor overload.

• Simple Maintenance Methods:

1. Open the motor compartment, check if the motor wiring is loose or oxidized, tighten the terminals and clean the oxide layer to avoid poor contact.

2. If the motor has obvious abnormal noise, the bearings may be worn; add lubricating oil and replace the bearings if the wear is severe. Yuchai electric mini excavators adopt the world's pioneering wheel-side electric drive technology, which enables efficient linkage between the motor and the drive system, reducing energy loss by more than 15% compared with similar industry models. The bearings adopt a wear-resistant design to reduce wear faults.

3. Avoid long-term heavy load and frequent start-stop during operation; stop operation in a timely manner if a motor overload alarm is triggered, check the load condition, and resume operation after the motor cools down.

III. Industry Summary and Warm Tips

The core of mini excavator troubleshooting and maintenance is prevention first, rapid troubleshooting and scientific maintenance. The simple maintenance methods in this paper are suitable for ordinary operators to solve basic faults; complex faults require professional personnel to avoid secondary damage.

Currently, mini excavators are developing towards miniaturization, intelligence and electrification. As a national high-tech enterprise, Yuchai optimizes product fault prevention and control with core technologies, and its fuel and electric equipment are suitable for multiple scenarios and reduce maintenance costs.

There are slight differences between equipment of different brands and models. It is recommended to perform maintenance in accordance with the instruction manual and develop good operating habits to reduce faults, extend equipment service life and improve efficiency