Hitachi EX135UR-5 Fault Code Insights

[MikePhua]

The Hitachi EX135UR-5, a compact yet versatile construction excavator, has been in production since the early 2000s under Hitachi’s renowned Zaxis series. Hitachi Construction Machinery, with roots in the Hitachi Group dating back decades, introduced the 135 UR alongside models like the ZX135 in response to growing demand for nimble utility excavators with hydraulic precision. While exact sales figures are proprietary, this class of machines typically sells thousands annually worldwide, especially across emerging markets in Asia and Europe.

Common Hydraulic Fault Codes
Some fault codes surface frequently in the EX135UR-5’s diagnostic system—triggering hydraulic lockout and persistent alarms:

• E81
  • Signifies a hydraulic pressure sensor or related control circuit failure.
    
  • Symptoms include hydraulic system lockout and continuous warning buzzer.
    
  • Likely causes: defective pressure sensor, wiring fault, or incorrect sensor alignment.
    
• E52
  • Points to malfunction within the hydraulic pump or its control circuit.
    
  • Can stem from low hydraulic fluid level, dirty or clogged filters, pump wear, or faulty pressure sensor wiring.
    

These codes are critical—when they occur, the machine’s movement functions may cease or become sluggish, which poses safety and productivity hazards.

Diagnosis and Resolution Strategies
To effectively respond to codes E52 or E81:

• Check hydraulic oil:
  • Confirm fluid is at proper level and free from contamination. Dirty fluid can degrade pressure sensor readings.
    
• Inspect filters:
  • Replace clogged filters promptly to ensure proper oil flow and pressure fidelity.
    
• Examine sensors and harnesses:
  • Look for bent pins, corrosion, or loose connections at the pressure sensor and its wiring harness.
    
• Test sensor output:
  • Use multimeter or diagnostic tools to verify voltage readings match factory specifications (E81 for sensor circuit anomalies).
    
• Replace faulty components:
  • If testing confirms sensor or circuit failure, swap in OEM sensor and recalibrate per manual.
    

Given the hydraulic system’s complexity and risk—especially under high-pressure conditions—it’s wise to engage certified technicians when in doubt.

Fault Code Workflow and Diagnostic Tools
Hitachi machines commonly feature self-diagnosis capabilities through tools like “Dr.EX.” This enables:

• Retrieval of current and stored fault codes.
  
• Real-time monitoring of sensor signals and solenoid outputs.
  
• Quick “retrial” to clear memory and check if issues persist after initial error.
  

A structured diagnostic approach is recommended:

1. Refer to technical manuals on troubleshooting sections (e.g., Fault-Code-A, symptom-based charts, wiring layout).
   
2. Use Dr.EX or equivalent diagnostic tool to read and clear codes.
   
3. Confirm whether codes reappear after retry.
   
4. Inspect components systematically based on fault type.
   
5. Repair or replace defective items, then validate repair by clearing codes and retesting.
   

Mini Anecdote
Consider a municipal maintenance crew in Australia operating an EX135UR-5 under scorching summer temperatures. One morning, the machine suddenly locked hydraulics, and the alarm blared—diagnosis revealed code E81. The crew inspected and found the hydraulic pressure sensor’s ground wire had deteriorated from heat cycles. A quick wire replacement and sensor check restored full hydraulic control—avoiding costly tow or downtime, and serving as a reminder that simple wiring often underlies alarm-triggering failures.

Terminology Glossary

• Hydraulic pressure sensor: Monitors oil pressure; its signal informs electronic controls.
  
• Hydraulic lockout: Safety mode where machine prevents movement due to detected fault.
  
• Self-diagnosis / Dr.EX: Hitachi’s system allowing fault code capture and live monitoring during operation.
  
• Retrial: Clearing stored codes to verify if malfunction is intermittent or resolved.
  
• OEM: Original equipment manufacturer—trusted source for replacement parts matching spec.
  

Repair Checklist Summary

• Check hydraulic fluid condition and level
  
• Replace dirty or clogged filters
  
• Inspect and test pressure sensor and wiring harness
  
• Use diagnostic tool to read and clear codes
  
• Replace defective sensors or wires as needed
  
• Retest under load to confirm resolution
  
• Document fault codes and fixes for maintenance records
  

Broader Context
Hitachi’s EX135UR-5 line reflects decades of expertise from the Hitachi brand—led by innovation, ruggedness, and intelligent control systems. Despite complex electronics, many reported faults like E52 or E81 trace back to simple elements: fluid contamination, aging wires, or sensor misalignment. Proactive maintenance, proper usage in high-heat environments, and vigilant diagnosis help preserve these excavators’ reliability.
When faults arise, prompt, informed action—not panic—lets operators keep their EX135UR-5 machines productive and safe, while honoring their strong mechanical heritage.