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Machine Overview
The Hitachi EX120 is a mid-sized hydraulic excavator produced in the mid-1990s, widely recognized for its reliable diesel engine, hydraulic system, and operator comfort. Designed for construction, earthmoving, and utility tasks, the EX120 typically features a 4-cylinder turbocharged diesel engine delivering around 90 horsepower, combined with a hydraulic travel system enabling smooth movement on tracked undercarriages.
Problem Description
The common concern with the 1996 EX120 involves the machine’s inability to travel—meaning it does not move when the travel levers are engaged, despite the engine running normally. This fault significantly limits the machine's functionality and requires systematic troubleshooting.
Key Troubleshooting Steps
The EX120’s hydraulic travel relies on proportional control valves modulating flow to the travel motors. Any interruption or miscommunication from sensors or loss of hydraulic pressure prevents system actuation. Maintaining cleanliness and hydraulic fluid quality is critical, as contamination leads to spool valve sticking or wear.
Glossary
Operators frequently report that replacing faulty pressure and angle sensors resolved no-travel issues. In some cases, cleaning or replacing hydraulic filters and flushing the system restored performance. Attention to wiring connectors ensured signal accuracy for travel commands.
One technician underscored the importance of methodical hydraulic pressure testing and sensor signal verification following electrical troubleshooting to isolate the root cause efficiently.
Additional Maintenance Tips
Travel failure in the 1996 Hitachi EX120 excavator commonly results from low pilot pressure, faulty sensors, or hydraulic circuit malfunctions. A systematic approach combining hydraulic pressure measurement, sensor testing, and electrical diagnostics is essential for effective repair. Maintaining hydraulic system cleanliness and adhering to preventive maintenance schedules reduces the likelihood of travel issues, ensuring machine reliability and productivity on job sites.
The Hitachi EX120 is a mid-sized hydraulic excavator produced in the mid-1990s, widely recognized for its reliable diesel engine, hydraulic system, and operator comfort. Designed for construction, earthmoving, and utility tasks, the EX120 typically features a 4-cylinder turbocharged diesel engine delivering around 90 horsepower, combined with a hydraulic travel system enabling smooth movement on tracked undercarriages.
Problem Description
The common concern with the 1996 EX120 involves the machine’s inability to travel—meaning it does not move when the travel levers are engaged, despite the engine running normally. This fault significantly limits the machine's functionality and requires systematic troubleshooting.
Key Troubleshooting Steps
- Check Pilot Hydraulic Pressure: The pilot pressure must be at least 750 psi to operate travel valves correctly. Low pilot pressure can cause the travel function to fail.
- Inspect Travel Pressure (DP) Sensor: Faulty sensors can send erratic signals to the control system, preventing travel actuators from engaging.
- Test Angle Sensor: The angle sensor feedback is crucial to the control logic of the travel system; a malfunctioning sensor may inhibit travel commands.
- Hydraulic Circuit Inspection: Verify hydraulic oil levels, filter cleanliness, and absence of leaks or blockages that could reduce flow or pressure.
- Control Valve and Solenoid Checks: Malfunctioning valves or solenoids in the travel circuit may cause travel failure.
- Electrical Diagnostics: Wiring harnesses, relays, and switches related to travel controls should be tested for continuity and proper operation.
The EX120’s hydraulic travel relies on proportional control valves modulating flow to the travel motors. Any interruption or miscommunication from sensors or loss of hydraulic pressure prevents system actuation. Maintaining cleanliness and hydraulic fluid quality is critical, as contamination leads to spool valve sticking or wear.
Glossary
- Pilot Pressure: Control hydraulic pressure used to operate servo valves and proportional controls.
- DP Sensor: Differential pressure sensor monitoring hydraulic pressures within the travel circuit.
- Angle Sensor: Device measuring the position or angle of travel levers or components for system feedback.
- Travel Valve: Hydraulic valve controlling flow to travel motors.
- Proportional Valve: Valve allowing variable flow control based on input signals, enabling speed modulation.
Operators frequently report that replacing faulty pressure and angle sensors resolved no-travel issues. In some cases, cleaning or replacing hydraulic filters and flushing the system restored performance. Attention to wiring connectors ensured signal accuracy for travel commands.
One technician underscored the importance of methodical hydraulic pressure testing and sensor signal verification following electrical troubleshooting to isolate the root cause efficiently.
Additional Maintenance Tips
- Regular hydraulic fluid analysis helps detect contamination or degradation early.
- Keeping hydraulic filters clean and replacing as per maintenance intervals prevents valve sticking.
- Electrical connectors should be inspected for corrosion or damage affecting sensor signals.
Travel failure in the 1996 Hitachi EX120 excavator commonly results from low pilot pressure, faulty sensors, or hydraulic circuit malfunctions. A systematic approach combining hydraulic pressure measurement, sensor testing, and electrical diagnostics is essential for effective repair. Maintaining hydraulic system cleanliness and adhering to preventive maintenance schedules reduces the likelihood of travel issues, ensuring machine reliability and productivity on job sites.
