Overview
The Kubota U48-4 and U55-4 Excavator Workshop Service Manual provides comprehensive technical documentation for maintenance, troubleshooting, inspection and component repair of these Kubota compact excavators. The workshop reference covers machine identification, engine construction, undercarriage assemblies, hydraulic pumps, control valves, swivel and travel motors, hydraulic cylinders, electrical systems and cabin equipment. Detailed mechanism and servicing information supports the diagnosis, disassembly, inspection, assembly and repair of the covered excavator components.
The documentation includes engine lubrication, cooling and fuel injection systems, rubber and steel crawler assemblies, hydraulic oil tank maintenance, load-sensing pump operation, pilot controls, auxiliary hydraulic circuits and electronic fault diagnosis. Separate hydraulic configurations are documented for the one-pump and three-pump load-sensing systems, including model-specific pump, control valve, travel motor and hydraulic hose arrangements. Electrical references cover instrument-panel diagnostics, automatic idling, anti-theft functions, CAN communication and auxiliary flow settings, while the Cabin section provides air-conditioning, refrigerant-system, window and wiper servicing information.
Notice: The hydraulic documentation identifies a one-pump load-sensing system for the U48-4 and a three-pump load-sensing system for the U55-4. Separate component and servicing procedures are provided for these configurations. Confirm the excavator identification and use the applicable hydraulic circuit, control valve, travel motor and hose-routing information before performing repairs.
Table of Contents
Kubota U48-4, U55-4 Manual
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01. Information and Safety
- Safety First and Workshop Safety Instructions
- Excavator Safety Decals and Warning Labels
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02. General Information and Maintenance
- Excavator Identification
- Engine Identification, Model Name and Serial Number
- E3B Engine Identification
- Engine Cylinder Number Identification
- General Workshop Precautions
- Electrical Wiring Handling Precautions
- Fuse and Electrical Connector Precautions
- High-Pressure Washing Precautions
- General Fastener and Stud Bolt Tightening Torques
- Hydraulic Hose Fitting Tightening Torques
- Hydraulic Elbow Lock-Nut and O-Ring Adaptor Torques
- Tapered Hydraulic Adaptor Specifications
- Hose Clamp Screw Tightening Torques
- European Version Product Features
- New Equipment Features and Technical Outline
- Machine Quality Specifications
- Water and Oil Quantity References
- Bucket Dimensions and Installation Measurements
- Rubber Crawler Specifications
- Steel Crawler Specifications
- Track Roller, Idler and Sprocket Information
- Hydraulic Cylinder Specifications
- Component Weight References
- Excavator Maintenance Checklist
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03. Machine Body and Undercarriage Servicing
- Front Operating Equipment
- Dozer Blade Dimensions
- Front Equipment Pins
- Swivel Frame Construction and Servicing
- Counterweight Disassembly and Assembly
- Fuel Tank Removal and Servicing
- Hydraulic Oil Tank Components
- Hydraulic Oil Return Filter Replacement
- Hydraulic Oil Suction Filter Replacement
- Hydraulic Oil Tank Breather Filter Replacement
- Hydraulic Tank Anti-Vibration Support Assembly
- Engine Mounting Components
- Engine Muffler Removal and Installation
- Air Cleaner and Supporting Structure
- Engine Radiator Components
- Hydraulic Oil Cooler Components
- Engine Accelerator Cable
- Travel Operating Lever Assembly
- Dozer Blade Operating Lever Assembly
- Track Frame Construction
- Swivel Bearing Assembly
- Rubber Track Removal and Installation
- Steel Track Removal and Installation
- Front Idler Disassembly and Assembly
- Front Idler Structural Components
- Track Tension Spring Assembly
- Track Frame Cylinder Assembly
- Track Roller Disassembly and Assembly
- Track Roller Structural Components
- Carrier Roller Disassembly and Assembly
- Carrier Roller Structural Components
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04. Engine — General, Mechanism and Servicing
- Engine Technical Specifications
- Engine Performance Curves
- Engine Dimensions
- Special Engine Service Tools
- Engine Construction and Features
- Cylinder Block Construction
- Engine Cooling Jacket
- Half-Floating Cylinder Head Cover
- Cylinder Head Construction
- Four-Screw Cylinder Assembly Structure
- Center Direct Injection System (E-CDIS)
- Engine Gear Train Configuration
- Piston Construction
- Engine Lubrication System
- Engine Oil Cooler
- Engine Cooling System
- Thermostat Construction and Operation
- Bottom Bypass Cooling System
- Fuel Injection System
- Engine Governor Mechanism
- Two-Stage Direct Injection Nozzle
- Fuel Injection Pump with F.S.P.
- CPV-Equipped Delivery Valve
- Engine Troubleshooting
- Engine Servicing Specifications
- General and Special Fastener Tightening Torques
- Engine Body Checking and Adjustment
- Lubricating System Checking and Adjustment
- Cooling System Checking and Adjustment
- Fuel System Checking and Adjustment
- Engine Electrical System Inspection
- Engine Oil and Coolant Draining
- External Engine Component Disassembly
- Cylinder Head and Valve Disassembly
- Thermostat Removal and Installation
- Injection Pump Unit Disassembly and Assembly
- Water Pump and Oil Cooler Disassembly
- Engine Front Cover Removal
- Flywheel and Timing Gear Disassembly
- Piston and Connecting Rod Removal
- Crankshaft and Crankcase Disassembly
- Starter Motor and Alternator Removal
- Cylinder Head and Valve Inspection and Servicing
- Timing Gear Inspection and Servicing
- Piston and Connecting Rod Servicing
- Crankshaft Inspection and Servicing
- Engine Cylinder Inspection
- Engine Oil Pump Servicing
- Engine Relief Valve Servicing
- Starter Motor and Alternator Servicing
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05. Hydraulic System — Mechanism and Servicing
- Complete Excavator Hydraulic Circuit Diagrams
- Hydraulic Component Layout and Identification
- One-Pump Load-Sensing System — U48-4
- Three-Pump Load-Sensing System — U55-4
- Load Pressure Detection System
- Automatic Travel Motor Speed Reduction
- Travel Motor Parking Brake System
- Hydraulic Pilot Pressure Operating System
- Variable Displacement Pump with Load-Sensing Control
- Variable Displacement Pump without Load-Sensing Control
- Hydraulic Gear Pump Construction
- Hydraulic Pump Specifications — U48-4
- Hydraulic Pump Components and Operation — U48-4
- Hydraulic Pump Specifications — U55-4
- Hydraulic Pump Components and Operation — U55-4
- Main Control Valve Specifications — U48-4
- Main Control Valve Hydraulic Circuit — U48-4
- Main Control Valve Construction and Operation — U48-4
- Main Control Valve Specifications — U55-4
- Main Control Valve Hydraulic Circuit — U55-4
- Main Control Valve Construction and Operation — U55-4
- Swivel Motor Construction and Operation
- Swivel Motor Components and Specifications
- Travel Motor Construction and Operation — U48-4
- Travel Motor Construction and Operation — U55-4
- Boom Hydraulic Cylinder Construction
- Arm Hydraulic Cylinder Construction
- Bucket Hydraulic Cylinder Components
- Front Equipment Swing Cylinder Components
- Dozer Blade Hydraulic Cylinder Components
- Boom, Arm, Bucket and Swivel Pilot Valve
- Travel Pilot Valve Construction and Operation
- Swing and Blade Pilot Valve Construction
- Hydraulic Unload Valve Construction and Operation
- Boom Holding Valve Construction and Operation
- Hydraulic Service Port Construction and Operation
- Hydraulic Pump Removal and Installation
- Hydraulic Pump Disassembly and Assembly
- Hydraulic Pump Disassembly Procedures — U48-4
- Hydraulic Pump Assembly Procedures — U48-4
- Hydraulic Pump Disassembly Procedures — U55-4
- Hydraulic Pump Assembly Procedures — U55-4
- Special Tools for Hydraulic Pump Servicing
- Hydraulic Pump Component Replacement Standards
- Main Control Valve Removal
- Control Valve Disassembly and Assembly — U48-4
- Control Valve Disassembly and Assembly — U55-4
- Swivel Motor Removal and Installation
- Swivel Motor Assembly Procedures
- Swivel Joint Removal and Installation
- Travel Motor Removal and Installation
- Travel Motor Disassembly and Assembly — U48-4
- Travel Motor Disassembly and Assembly — U55-4
- Special Tools for Travel Motor Servicing
- Hydraulic Cylinder Disassembly and Assembly
- Hydraulic Cylinder Component Inspection
- Main Control Pilot Valve Disassembly and Assembly
- Pilot Valve U-Joint Tightening Tool
- Travel Pilot Valve Disassembly and Assembly
- Blade and Swing Pilot Valve Disassembly and Assembly
- Hydraulic Unload Valve Disassembly and Assembly
- Third-Line Valve Assembly Components
- Third-Line Hydraulic Hose Routing
- High-Pressure Hydraulic Hose Specifications
- Hydraulic Delivery Hose Routing — U48-4
- Hydraulic Delivery Hose Routing — U55-4
- Hydraulic Hose Clamp Positions
- Hydraulic Suction Pipe and Hose Routing
- Front Equipment Hydraulic Hose Routing
- Travel, Swivel, Blade and Swing Hose Routing — U48-4
- Travel, Swivel, Blade and Swing Hose Routing — U55-4
- Swivel Joint and Travel Motor Hose Routing
- Track Frame Hydraulic Hose Routing
- Low-Pressure Hydraulic Hose and Protective Tube Specifications
- Hydraulic Drain Hose Routing — U48-4
- Hydraulic Drain Hose Routing — U55-4
- Pilot Hydraulic Hose Specifications
- Pilot Pressure and Return Hose Routing
- Front Equipment Pilot Hose Routing
- Travel, Blade, Swing and Auxiliary Pilot Hose Routing
- Main Control Valve Pilot Hose Connections
- Pilot Hose Routing Around the Operator Seat
- Boom Holding Valve Disassembly and Assembly
- Boom Holding Valve Release Procedure
- Hydraulic Component Performance Measurement
- Hydraulic System Troubleshooting
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06. Electrical System and Electronic Diagnostics
- Electronic Component Layout
- Electrical Wiring Circuit
- Electrical Wiring Clamp Precautions
- Electrical Connector Handling and Disconnection
- Electrical Wiring Layout
- Starting Equipment Troubleshooting
- Electrical Power and Ground Inspection
- Engine Starting and Stopping Device Inspection
- Instrument Panel Operating Guide
- Meter Console Controls and Functions
- Hour Meter and Clock Display
- Engine Speed, Coolant Temperature and Fuel Display
- Machine Operating Information Display
- Periodic Maintenance Confirmation Functions
- Instrument Panel Clock Settings
- Time Format Selection
- Instrument Panel Language Selection
- Anti-Theft System Settings
- Refuelling Buzzer Settings
- Auxiliary Hydraulic Port Operating Modes
- Auxiliary Port Handling Procedures
- Auxiliary Hydraulic Maximum Flow Settings
- Service Dealer Diagnostic Settings
- Instrument Panel Warning and Alarm Displays
- Meter Panel Troubleshooting
- Engine Oil Pressure Error Diagnosis
- Charging System Error Diagnosis
- Fuel Sensor Error Diagnosis
- Coolant Temperature Sensor Error Diagnosis
- Operating Lever Lock System Diagnostics
- Two-Speed Travel System Diagnostics
- Automatic Idling (AI) System
- Governor Sensor Error Diagnosis
- Accelerator Sensor Error Diagnosis
- Automatic Idling Motor Diagnostics
- Automatic Idling Pressure Switch Testing
- Automatic Idling Switch Testing
- Anti-Theft (AT) System Troubleshooting
- Electrical Overvoltage Diagnosis
- 5V and 12V Short-Circuit Diagnosis
- CAN Communication Error Diagnosis
- AUX1 and AUX2 System Troubleshooting
- Hydraulic Holding Valve Electrical Diagnostics
- Battery Isolator Diagnostics
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07. Cabin — Air Conditioning and Servicing
- Cabin Air Conditioning System Construction
- Air Conditioning Operating Principles
- Air Conditioning Compressor
- Cabin Air Conditioning Unit
- Refrigerant Condenser and Receiver
- Air Conditioning Pressure Switch
- Cabin Climate Control Functions
- Airflow and Vent Direction Adjustment
- Air Conditioning Electrical Circuits
- Cabin Air Conditioning Relays
- Blower Switch and Motor Operation
- Windshield Wiper Switch
- Windshield Wiper and Wiper Motor
- Cabin Air Conditioning Troubleshooting
- Maintenance and Servicing Specifications
- Cabin Component Tightening Torques
- Refrigerant System Repair Precautions
- Manifold Gauge and Refrigerant Service Tools
- Refrigerant Recovery and Recycling Equipment
- Refrigerant Pressure Inspection
- Refrigerant Recovery and System Evacuation
- High-Pressure-Side Refrigerant Charging
- Low-Pressure-Side Refrigerant Charging
- Refrigerant System Inspection and Troubleshooting
- Compressor Checking and Adjustment
- Air Conditioning Relay Inspection
- Blower Motor and Resistor Inspection
- Blower Switch Checking
- Temperature Control Servo Motor Testing
- Air Conditioning Pressure Switch Inspection
- Air Conditioning Hose Connection and Removal
- Compressor Removal and Installation
- Refrigerant Receiver Removal and Installation
- Air Conditioning Duct Removal and Installation
- Cabin Air Inlet Removal and Installation
- Cabin Removal and Mounting
- Windshield Washer System
- Wiper and Washer Motor Servicing
- Cabin Working Light and Interior Light
- Cabin Glass Removal and Installation
- Window Glass Trim Types
- Front Window Closing Lock Adjustment
- Front Window Opening Lock Adjustment
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Electrical Diagrams — Appendix
- Electrical Wiring Diagram
- Electrical Circuit Diagram
Load-Sensing Hydraulic Configurations and Electronic Fault Diagnosis
The hydraulic workshop information distinguishes the U48-4 one-pump load-sensing arrangement from the U55-4 three-pump system. These differences extend to hydraulic pump construction, main control valves, travel motors and associated hose routing. The documentation also provides performance measurement procedures, pump component replacement standards, boom holding-valve servicing and individual pilot control-valve repairs. When investigating hydraulic performance or replacing components, the relevant system configuration and connection diagrams should be identified before testing or disassembly.
The electrical section provides instrument-panel diagnostic functions, warning displays, automatic idling controls, auxiliary hydraulic flow settings and CAN communication troubleshooting. These references support investigation of operating faults involving the engine, hydraulic controls and electronic equipment. Cabin servicing is documented separately, including refrigeration-system pressure testing, component inspections and window mechanisms, allowing electrical and mechanical problems to be assessed using the corresponding workshop procedures.
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