Komatsu PC60 Fuse 2 Failure and Electrical Short Tracing

[MikePhua]

The Komatsu PC60 and Its Electrical System Layout
The Komatsu PC60 is a compact hydraulic excavator introduced in the late 1980s and refined through the 1990s, designed for urban excavation, trenching, and light demolition. With an operating weight around 6 metric tons and powered by a four-cylinder Komatsu or Mitsubishi diesel engine, the PC60 became popular for its mechanical simplicity and reliability. Its electrical system is built around a fuse panel located near the operator’s seat or under the right-side console, protecting circuits for lighting, sensors, solenoids, and control modules.
Terminology annotation:

• Fuse 2: A specific fuse in the panel, typically rated at 10–15 amps, responsible for powering key circuits such as fuel shutoff solenoids, gauges, or relays.
  
• Short to Ground: An unintended electrical path where current flows directly to chassis ground, causing excessive amperage and fuse failure.
  
• Solenoid Coil: An electromagnetic actuator that opens or closes valves or switches when energized.
  
• Harness Chafing: Physical wear on wire insulation due to vibration, rubbing, or heat exposure, often leading to shorts.
  

In Wisconsin, a contractor reported repeated Fuse 2 failures on his PC60. The fuse would blow immediately upon key-on, disabling the fuel solenoid and preventing engine start. After replacing the fuse multiple times, he began tracing the wiring manually.
Symptoms and Initial Diagnostic Steps
When Fuse 2 blows consistently, it indicates a direct short or overload in one of the protected circuits. Common symptoms include:

• Engine cranks but does not start
  
• No power to fuel shutoff solenoid
  
• Dashboard gauges inactive
  
• Audible click from relay panel missing
  
• Fuse blows instantly when ignition is turned on
  

Diagnostic checklist:

• Identify all components powered by Fuse 2 using wiring diagram
  
• Disconnect fuel solenoid and test fuse behavior
  
• Inspect wire harness from fuse panel to solenoid and sensors
  
• Use multimeter to check resistance to ground from fuse output terminal
  
• Look for melted insulation, pinched wires, or exposed copper
  

Recommendations:

• Replace fuse with same amperage rating only
  
• Disconnect suspect components one at a time to isolate fault
  
• Use test light to confirm voltage presence after fuse replacement
  
• Label wires during inspection to avoid misrouting
  

In British Columbia, a technician found that the fuel solenoid wire had rubbed against the engine block, exposing copper and shorting to ground. Wrapping the wire in heat-resistant loom and rerouting it resolved the issue permanently.
Common Failure Points and Wire Routing Hazards
Older Komatsu machines often suffer from harness degradation due to age, heat, and vibration. Fuse 2 typically powers circuits that run near the engine, making them vulnerable to abrasion and oil contamination.
Known failure points:

• Fuel shutoff solenoid wire near starter motor
  
• Harness junction under operator seat
  
• Relay panel connectors with corroded terminals
  
• Sensor wires near hydraulic pump housing
  
• Ground strap connections with poor contact
  

Inspection tips:

• Remove seat and side panels for full harness access
  
• Use flashlight and mirror to inspect behind engine block
  
• Wiggle wires while monitoring fuse behavior
  
• Check for aftermarket splices or repairs with electrical tape
  

Recommendations:

• Replace damaged wires with marine-grade tinned copper
  
• Use heat shrink tubing and waterproof connectors
  
• Secure harness with rubber-lined clamps every 30 cm
  
• Add split loom to exposed sections near heat sources
  

In Texas, a fleet manager retrofitted his PC60 units with upgraded harnesses using silicone-insulated wire. This eliminated recurring fuse failures and improved reliability in high-heat trenching operations.
Solenoid Coil Resistance and Relay Behavior
The fuel shutoff solenoid is a common culprit in Fuse 2 failures. If the coil inside the solenoid shorts internally, it can draw excessive current and blow the fuse even without visible damage.
Testing procedure:

• Disconnect solenoid and measure coil resistance (typically 10–30 ohms)
  
• Check for continuity between coil terminals and solenoid body
  
• Apply 12V power briefly and listen for click
  
• Inspect relay controlling solenoid for stuck contacts or melted housing
  

Recommendations:

• Replace solenoid if resistance is below 5 ohms or shows continuity to ground
  
• Test relay with jumper wires and confirm switching behavior
  
• Use OEM solenoids with proper amperage rating
  
• Avoid energizing solenoid continuously during diagnostics
  

In Georgia, a contractor replaced a fuel solenoid that measured only 2.1 ohms. The new unit restored normal fuse behavior and eliminated intermittent shutdowns.
Preventative Measures and Electrical System Longevity
To prevent future Fuse 2 failures:

• Inspect harness annually for wear and corrosion
  
• Replace fuses with slow-blow type only if specified by manufacturer
  
• Clean and tighten ground connections quarterly
  
• Avoid pressure washing near fuse panel or relay box
  
• Document wire repairs and component replacements in service log
  

Recommendations:

• Add inline fuse holders with waterproof caps for field diagnostics
  
• Use dielectric grease on connectors exposed to moisture
  
• Train operators to report electrical faults immediately
  
• Keep spare fuses, relays, and solenoids in field kit
  

In Alaska, a utility crew added fuse panel covers with silicone seals to all PC60 units. This reduced moisture intrusion and extended fuse life during winter operations.
Conclusion
Fuse 2 failures in the Komatsu PC60 are often caused by shorts in the fuel solenoid circuit, degraded wiring, or faulty relays. While the fuse itself is a symptom, the root cause lies in insulation, routing, and component integrity. With structured diagnostics, careful inspection, and preventative upgrades, the issue can be resolved and avoided. In compact excavators, power isn’t just hydraulic—it’s electrical. And when the fuse pops, the fix begins with wire, resistance, and vigilance.