Hitachi EX60-1 EP Control Failure and Electrical Recovery Strategy

[MikePhua]

When the EP (Electronic Power) control system on a Hitachi EX60-1 fails to increase engine RPM after startup, the root cause often lies in damaged wiring, blown fuses, or compromised grounding. These faults can be triggered by rodent damage, corrosion, or improper repairs, and they disrupt the signal path between the EP switch, timer relay, and engine control solenoid.
Hitachi EX60-1 Background and EP System Design
The Hitachi EX60-1 was introduced in the early 1990s as part of Hitachi’s compact excavator lineup. Designed for urban construction, utility trenching, and light demolition, the EX60-1 features a 6-ton operating weight, a 4-cylinder Isuzu diesel engine, and a hydraulically actuated boom and arm system. The EP control system was an early attempt to electronically modulate engine RPM based on operator input, improving fuel efficiency and responsiveness.
The EP system includes a dashboard-mounted switch, a timer relay, a 10A fuse, and a solenoid actuator that adjusts the throttle linkage. When functioning correctly, pressing the EP button increases engine RPM to match hydraulic demand. However, the system is sensitive to wiring faults and grounding issues.
Terminology Note

• EP Control: Electronic Power control system that adjusts engine RPM based on operator input.
  
• Timer Relay: A delay circuit that manages EP signal timing and solenoid activation.
  
• Solenoid Actuator: An electromechanical device that moves the throttle linkage when energized.
  
• Ground Wire: A conductor that completes the electrical circuit and stabilizes voltage.
  
• Grey Market Machine: An imported unit not originally intended for the local market, often lacking documentation or support.
  

Failure Sequence and Observations
The machine operated normally for over 1500 hours before a mouse chewed through four wires near the timer relay. After replacing the wires and installing a new 10A fuse, the EP system worked briefly during the first startup. However, on the second attempt, the fuse blew again, and the EP button stopped responding.
A loose ground wire was discovered and tightened before the second startup. This may have contributed to the fuse failure or disrupted the EP signal path. The solenoid actuator did not respond to EP input, and engine RPM remained static.
Diagnostic Strategy and Repair Recommendations

• Inspect all wiring near the timer relay. Rodent damage often affects multiple wires, including signal and ground paths. Use a multimeter to check continuity and voltage.
  
• Replace the 10A fuse only after confirming no short circuits. Repeated fuse failure indicates unresolved electrical faults.
  
• Test the EP switch output. Use a voltmeter to confirm signal voltage when the button is pressed.
  
• Check the solenoid actuator for mechanical binding or electrical failure. Apply direct voltage to confirm movement.
  
• Verify ground integrity. A poor ground can cause voltage spikes or incomplete signal paths, leading to fuse blowouts.
  
• Use a wiring diagram if available. Grey market machines may differ from domestic models, so trace each wire manually if necessary.
  

Field Experience and Anecdotes
In Malaysia, an operator restored EP function on an EX60-1 by replacing the timer relay and re-grounding the instrument panel. He noted that the machine ran fine for one cycle but failed again due to a missed wire splice. After rechecking all connections and replacing the solenoid, the EP system returned to normal.
In New Zealand, a technician working on a grey-market EX60-1 found that the EP system had been bypassed entirely. The throttle was manually adjusted, and the EP button was disconnected. He rebuilt the circuit using a donor relay and restored full electronic control.
Conclusion
EP control failure on the Hitachi EX60-1 is often caused by wiring damage, poor grounding, or solenoid malfunction. While the system is simple in design, its reliability depends on clean electrical paths and stable voltage. For grey market machines, manual tracing and component testing are essential. With careful inspection and targeted repairs, EP functionality can be restored, improving fuel efficiency and operator control.