Komatsu PC120 Hydraulic Excavator No-Start Issue and Specifications

[MikePhua]

Overview of the Komatsu PC120
The Komatsu PC120 is a medium hydraulic excavator widely used in construction, landscaping, and utility projects worldwide due to its reliable performance and efficient hydraulic system. The standard PC120 model features an operating weight of around 26,500 lbs (12,030 kg) and is powered by a reliable 87-90 horsepower turbocharged diesel engine (such as the Komatsu S4D105-5 or Isuzu 6BG1), delivering strong digging and operational capacity for various tasks.
Key dimensions include:

• Maximum digging height approximately 28 feet 3 inches.
  
• Maximum digging depth around 18 feet.
  
• Maximum reach length near 27 feet.
  
• Tail swing radius between 7 to 8 feet.
  
• Bucket digging force near 18,700 lbs and arm crowd force about 13,900 lbs.
  

The machine’s hydraulic system includes variable displacement pumps delivering flow rates up to 85 gallons per minute under pressure around 2,500 psi, allowing smooth boom and arm operation with high breakout forces.
No-Start Problem Insights
A no-start issue on the Komatsu PC120 excavator can stem from various causes ranging from electrical to fuel system failures:

• Electrical System: Battery condition, starter motor functionality, and wiring continuity must be inspected. Faulty ignition switches, relays, or fuses can prevent engine cranking.
  
• Fuel Delivery Problems: Clogged fuel filters, air in the fuel lines, or malfunctioning fuel pumps can prevent fuel from reaching the engine.
  
• Glow Plug or Preheat System Failure: In cold conditions, defective glow plugs or wiring can hinder cold starts.
  
• Engine Sensors and ECU: Faulty sensors (such as crankshaft position or camshaft position sensors), or Electronic Control Unit (ECU) errors may inhibit fuel injection or spark timing.
  
• Hydraulic Lock or Mechanical Issues: Rare conditions like hydraulic lock or seized components might physically prevent the engine from turning over.
  

Troubleshooting Approach

1. Battery and Starter Check: Confirm voltage levels and starter engagement. Replace or recharge batteries if low.
   
2. Fuel System Inspection: Drain filters, bleed fuel lines, and verify fuel pump operation.
   
3. Electrical Testing: Use a multimeter to test ignition circuit continuity and sensor outputs.
   
4. Glow Plug Test: Inspect glow plugs for resistance; replace if faulty.
   
5. Error Code Diagnostics: Connect diagnostic tools to retrieve ECU fault codes.
   
6. Mechanical Movement: Attempt to manually rotate the engine or inspect for compression-related issues.
   

Terminology

• Glow Plug: A heating element that warms diesel combustion chambers for easier starting.
  
• Breakout Force: The force applied by the excavator’s bucket edge to break into material.
  
• Variable Displacement Pump: A hydraulic pump capable of modulating output flow to maximize efficiency.
  
• Hydraulic Lock: Condition where hydraulic fluid pressure prevents engine crankshaft rotation.
  
• Electronic Control Unit (ECU): The onboard computer controlling engine functions including fuel injection and ignition.
  

Additional Advice
Many operators report that preventive maintenance, such as regular replacement of filters and batteries, significantly reduces start-up failures. Awareness of the diagnostic LED indicators and service manuals specific to the PC120 model aids more efficient troubleshooting.
Industry Scenario
In a notable case, a construction firm experienced intermittent no-starts in their PC120 during cold months. Diagnosing a faulty fuel shutoff solenoid resolved the problem, restoring reliable startups and minimizing operational delays.
Summary
Komatsu PC120 no-start conditions require systematic evaluation of electrical, fuel, and mechanical systems to isolate faults. Understanding machine specifications, hydraulic capabilities, and associated components supports effective problem resolution. Regular preventive care and utilization of diagnostic tools are essential to maintaining readiness and uptime for this popular excavator.