Diagnosing Swing Function Failure on the Komatsu PC200LC-6 Excavator

[MikePhua]

Komatsu’s PC200LC-6 and Its Legacy in Earthmoving
The Komatsu PC200LC-6 is part of the sixth-generation hydraulic excavator series introduced in the 1990s, a period when Komatsu was rapidly expanding its global footprint. Known for its balance of power, reliability, and serviceability, the PC200LC-6 became a staple in construction, mining, and utility sectors. With an operating weight around 20 metric tons and powered by a Komatsu S6D102E diesel engine, it features a load-sensing hydraulic system and electronically monitored control panel.
The “LC” designation refers to its long carriage, offering improved stability during trenching and lifting operations. Thousands of units were sold globally, and many remain in service today, especially in regions where mechanical simplicity is valued over digital complexity.
Swing Function Failure and Initial Observations
A recurring issue on aging PC200LC-6 machines is the sudden loss of swing function. In one documented case, the operator noted that the excavator’s swing stopped abruptly without any noise or warning. The engine bogged slightly when attempting to swing, indicating that hydraulic pressure was being applied but the house wouldn’t rotate. This behavior often mimics a stuck swing brake or failed solenoid.
Key symptoms include:

• No swing movement despite audible engine load
  
• All other hydraulic functions operating normally
  
• Override switch ineffective
  
• Diagnostic codes present but unrelated to swing
  

These signs suggest either an electrical control fault or a mechanical failure in the swing brake release system.
Understanding the Swing Brake System
The swing brake on the PC200LC-6 is spring-applied and hydraulically released. When the operator commands a swing, the control system energizes a solenoid that allows hydraulic pressure to release the brake. If the solenoid fails, or if pressure is not reaching the brake piston, the brake remains engaged and prevents rotation.
The swing brake timer is embedded in the machine’s computer, and the override switch is designed to bypass this logic. If the override fails to release the brake, the issue may lie in the solenoid coil, wiring harness, or hydraulic circuit.
Electrical Diagnostics and Solenoid Testing
The swing solenoid typically operates at 24 volts and should show approximately 7 ohms of resistance across its terminals. In this case, the solenoid was replaced and tested with direct voltage application. The coil clicked audibly when energized with the engine off, but no change occurred during operation.
Recommended steps:

• Use a multimeter to verify coil resistance
  
• Apply 24V directly to the solenoid and observe response
  
• Inspect fuse panel for blown or corroded fuses
  
• Check wiring harness for abrasion, corrosion, or loose connectors
  
• Confirm voltage delivery at the solenoid during swing command
  

If the solenoid is functional and receiving voltage, the fault may lie deeper in the hydraulic circuit or mechanical assembly.
Hydraulic Pressure Testing and Gear Reducer Inspection
To confirm whether hydraulic pressure is reaching the swing brake release port, a pressure gauge and tee fitting should be installed in the line. If pressure is absent or insufficient, the issue may be a blocked valve, failed pump output, or internal leakage.
Another possibility is mechanical failure inside the swing gear reducer. Broken brake components, seized bearings, or debris in the housing can prevent rotation even if the brake is released.
Inspection steps:

• Drain gear oil and check for metal shavings or contamination
  
• Rotate the swing motor manually to detect resistance
  
• Remove access covers and inspect brake piston and springs
  
• Verify gear backlash and bearing integrity
  

If internal damage is found, the gear reducer may require a full rebuild or replacement.
Anecdote from Nova Scotia
An operator in Nova Scotia experienced a similar issue on his PC200LC-6. After replacing the swing solenoid and confirming electrical continuity, he applied 24V directly to the coil and heard it click—but the house still wouldn’t rotate. Suspecting a mechanical fault, he drained the gear oil and discovered fragments of a broken brake spring. The swing brake had failed internally, locking the house in place. After sourcing replacement parts from a salvage yard, he rebuilt the brake assembly and restored full function.
Recommendations for Long-Term Reliability
To prevent swing failures and maintain system integrity:

• Inspect swing brake solenoid and wiring every 500 hours
  
• Replace hydraulic filters and test pressure quarterly
  
• Drain and replace gear oil annually, checking for contamination
  
• Use dielectric grease on connectors exposed to moisture
  
• Keep a log of fault codes and service actions
  

For machines operating in cold or wet climates, consider installing protective covers over solenoids and connectors to reduce corrosion risk.
Conclusion
Swing function failure on the Komatsu PC200LC-6 is often a blend of electrical and mechanical issues. While solenoid replacement may resolve some cases, deeper faults in the brake assembly or hydraulic circuit require methodical diagnosis. With proper testing tools, service discipline, and awareness of system architecture, operators can restore swing capability and extend the life of this iconic excavator. In the world of heavy iron, rotation is more than movement—it’s momentum, and every degree counts.