Komatsu PC138US-11 Loses All Pilot Function When Warm
Fault Codes & Symptoms
No response to any joystick or travel pilot controls. Related symptoms: - Delayed or slow pilot response before complete failure. - Whining noise from the hydraulic pump area as the pump cavitates. Machine works fine for 15-30 minutes, then all controls (joysticks, travel levers) stop responding completely. If the machine is shut down and cools off, it works again for a while.
Confirmed cause: The internal suction strainer for the pilot pump was severely clogged with fine debris. When the hydraulic oil was cold and thick, the pump could still pull enough oil to build pressure. As the oil heated up and thinned, it bypassed the debris more easily, causing the pump to cavitate and lose its prime. Repair performed: Removed the pilot pump. Accessed and replaced the clogged internal suction strainer. Reinstalled the pump and filled with clean hydraulic fluid. Verification: The machine was operated for over two hours, performing various functions including travel, digging, and swinging. The machine was brought to full operating temperature and allowed to heat soak. All pilot functions remained responsive with no loss of control. Technician notes: - This fault mimics an electrical issue or a major leak, but the key was checking for flow, not just pressure, at the pump outlet. - The debris in the screen was non-metallic and resembled degraded seal material, suggesting another component may be failing elsewhere in the system. Recommended monitoring hydraulic filters closely. - Accessing the pilot pump and its internal strainer requires removing several belly pans and working in a tight space.