Hitachi EX165 Fast Tracking Issues: Diagnosing Intermittent High-Speed Travel Failures

[MikePhua]

Introduction
The Hitachi EX165 excavator, known for its reliability and performance in mid-sized earthmoving operations, occasionally presents challenges in its two-speed travel system. A common issue reported by operators is intermittent failure when switching to high-speed tracking mode—where the machine jumps between low and high speeds or fails to engage fast travel altogether. This article explores the underlying mechanics of the two-speed system, clarifies key terminology, and offers diagnostic strategies, field anecdotes, and practical solutions for resolving fast tracking inconsistencies.
Understanding the Two-Speed Travel System
The EX165 features a hydraulic travel motor with a variable swash plate that adjusts between low and high-speed modes. The transition is controlled by pilot pressure delivered via solenoid valves, which are activated by the operator’s travel speed switch.
Key components include:

• Travel Speed Solenoid (SI): Controls pilot oil flow to the travel motor for high-speed engagement.
  
• Swing Motor Pressure Switch: Detects travel pressure; must be active for fast mode to engage.
  
• Front Attachment Switch: Must be off to allow high-speed travel.
  
• Pump Delivery Pressure Sensors: Monitor hydraulic output; both must be functional for fast tracking to activate.
  

Terminology Clarified

• Swash Plate: A component inside the hydraulic motor that changes the angle of piston stroke, controlling speed and torque.
  
• Pilot Oil: Low-pressure hydraulic fluid used to actuate control valves and directional functions.
  
• Solenoid Valve: An electrically controlled valve that directs hydraulic flow based on input signals.
  
• Fast Tracking Mode: High-speed travel setting used for moving across large job sites or fields.
  

Common Causes of Intermittent Fast Travel

• Faulty Solenoid (SI)
  If the SI solenoid fails or receives inconsistent voltage, the swash plate may not shift properly, causing the machine to revert to low speed.
  
• Damaged Wiring or Connectors
  Power washing the cab or prolonged exposure to moisture can corrode connectors behind the operator seat, disrupting signal flow.
  
• Incorrect Pressure Switch Behavior
  The green travel pressure switch must be active during movement, while the blue front attachment switch must remain off. Misbehavior in either can block fast travel.
  
• Sensor Malfunction
  If either pump delivery pressure sensor fails, the system may prevent high-speed engagement as a safety precaution.
  

Field Anecdote: Irish Excavator Troubleshooting
A fleet technician in Ireland reported that a Hitachi EX165 tracked reliably in low speed but jumped erratically when switched to high. After replacing a green pressure switch on the swing motor with no improvement, he investigated the solenoids marked SI, SO, and SW. Upon disconnecting and inspecting the plugs behind the seat—damaged by frequent cab washing—the machine resumed normal operation temporarily. The issue later returned, coinciding with signs of oil mixing into the coolant, suggesting broader hydraulic contamination.
Historical Context: Hitachi’s Travel Control Evolution
Hitachi’s two-speed travel systems evolved in the 1990s to improve jobsite mobility. Early models relied heavily on pilot pressure and basic electrical inputs, making them vulnerable to wiring degradation and sensor misalignment. Later models introduced more robust diagnostics and sealed connectors, but legacy units like the EX165 still require manual troubleshooting and component familiarity.
Case Study: New Zealand Solenoid Identification
A technician in New Zealand confirmed that solenoid SI typically controls fast travel and should receive a 24V signal when activated. He emphasized that both pump pressure sensors must be operational for the system to allow fast mode. This insight helped another operator bypass faulty wiring by installing a manual switch directly to the SI solenoid—though such modifications should be approached cautiously to avoid safety risks.
Best Practices for Diagnosing Fast Travel Failures

• Inspect and clean all solenoid connectors, especially behind the operator seat
  
• Test voltage supply to the SI solenoid during travel switch activation
  
• Verify pressure switch behavior using a multimeter or diagnostic software
  
• Check for hydraulic contamination that may affect valve response
  
• Avoid power washing sensitive electrical areas without protective sealing
  
• Consult wiring diagrams to trace signal paths and confirm solenoid roles
  

Recommended Tools and Techniques

• Multimeter: For checking voltage and continuity at solenoid terminals
  
• Hydraulic Pressure Gauge: To verify pilot pressure delivery
  
• Service Manual Diagrams: Essential for identifying solenoid functions and wire colors
  
• Dielectric Grease: Protects connectors from moisture and corrosion
  

Conclusion
Intermittent fast tracking issues in the Hitachi EX165 often stem from electrical faults, solenoid misbehavior, or sensor misalignment. By understanding the system’s architecture, clarifying terminology, and applying field-tested diagnostics, technicians can restore reliable high-speed travel and improve machine productivity. In excavators where mobility matters, smooth transitions between speed modes aren’t just a convenience—they’re a cornerstone of efficient operation.