Why Does the Komatsu PW150ES-6K Lose Power in Drive

[MikePhua]

The PW150ES-6K and Komatsu’s Wheeled Excavator Lineage
The Komatsu PW150ES-6K is a mid-size wheeled excavator designed for urban infrastructure, roadwork, and utility trenching. Part of Komatsu’s PW series, this model combines hydraulic precision with on-road mobility, making it ideal for contractors who need to travel between job sites without a trailer. Komatsu, founded in 1921 in Japan, has built a reputation for durable earthmoving equipment, and its wheeled excavators are especially popular in Europe and Asia.
The PW150ES-6K features a hydrostatic drive system powered by a variable displacement hydraulic pump and dual travel motors. Unlike tracked excavators, wheeled models rely heavily on hydraulic modulation and electronic control to manage torque and speed across varying terrain.
Terminology Notes

• Hydrostatic Drive: A propulsion system using hydraulic fluid to transmit power from the engine to the wheels via motors.
  
• Travel Motor: A hydraulic motor that drives the wheels or tracks of an excavator.
  
• Drive Interruptions: Sudden loss or fluctuation in propulsion, often felt as jerks or stalls.
  
• Load Sensing System: A hydraulic control system that adjusts flow and pressure based on demand, improving efficiency.
  

Reported Symptoms and Initial Repairs
In one case, a PW150ES-6K exhibited no power in forward or reverse drive, despite both travel motors being overhauled. The machine would jerk under load, suggesting intermittent hydraulic engagement. These symptoms point to a deeper issue beyond motor wear—likely involving control valves, pressure sensors, or electronic modulation.
Potential Causes and Diagnostic Path

1. Hydraulic Control Valve Malfunction
   The travel control valve may be sticking or leaking internally, preventing consistent pressure delivery. Inspect spool movement and check for contamination or scoring.
   
2. Electronic Modulation Failure
   The travel motors are often regulated by solenoids and sensors. A faulty speed sensor or PWM signal interruption can cause erratic drive behavior. Use a diagnostic tool to scan for fault codes and verify voltage at the solenoids.
   
3. Pressure Drop in Load Sensing Circuit
   If the load sensing line is blocked or leaking, the pump may not ramp up pressure under demand. Check the pilot pressure and verify that the pump responds to joystick input.
   
4. Pump Swash Plate Sticking
   In variable displacement pumps, the swash plate angle determines flow rate. If the plate is stuck or the actuator fails, the pump may not deliver sufficient flow for travel.
   
5. Hydraulic Fluid Contamination or Aeration
   Dirty or foamy fluid can reduce system responsiveness. Inspect filters, fluid condition, and tank breather. Replace fluid if signs of water or air are present.
   

Recommendations for Troubleshooting

• Perform a pressure test at the travel motor inlet during operation to confirm flow and pressure
  
• Check solenoid resistance and voltage at the travel control valve
  
• Inspect pilot lines and joystick response for lag or dead zones
  
• Use Komatsu’s diagnostic interface to scan for electronic faults
  
• Replace hydraulic filters and fluid if contamination is suspected
  

Conclusion
Loss of drive power in the Komatsu PW150ES-6K is rarely caused by the travel motors alone. When jerking and power loss persist after motor overhaul, the issue likely lies in the hydraulic control system or electronic modulation. A methodical diagnostic approach—combining pressure testing, sensor verification, and fluid inspection—can uncover hidden faults and restore reliable travel performance.