What is Komatsu PC240LC-10 Fault Code H-31?

Fault Code H-31 on the Komatsu PC240LC-10 indicates a hydraulic pump torque control system malfunction, specifically an abnormal signal from the pump flow control solenoid or its associated circuitry. This code triggers when the Electronic Control Module (ECM) detects voltage irregularities, circuit continuity issues, or mechanical failures in the pump torque control solenoid valve that regulates hydraulic pump displacement based on engine load.

This fault is critical because the pump torque control system directly affects fuel efficiency and prevents engine stalling under heavy hydraulic loads. When H-31 activates, the excavator's computerized load-sensing system cannot properly match hydraulic pump output to operational demands, leading to performance degradation and potential component damage on used machines with accumulated wear.

Common Symptoms

• Reduced hydraulic power across all functions (boom, arm, bucket, swing) with noticeably sluggish response times
• Engine rpm fluctuations or unexpected stalling during combined multi-function operations
• Hydraulic system overheating due to improper pump displacement regulation
• Warning light activation on the monitor panel with simultaneous code storage in the ECM
• Erratic hydraulic flow that improves temporarily after machine restart but returns under load

Potential Causes

The most common technical reasons for H-31 on used PC240LC-10 excavators include:

• Pump torque control solenoid valve failure due to internal coil breakdown or stuck spool (common after 6,000+ operating hours)
• Wiring harness damage at known rub points near the hydraulic pump mounting area where vibration causes insulation wear
• Connector corrosion at the 6-pin solenoid connector, especially on machines operated in wet/coastal environments
• ECM voltage supply issues caused by deteriorated main power harness connections or failing alternator output
• Contaminated hydraulic oil causing solenoid valve sticking or debris accumulation in control passages

How to Troubleshoot and Fix Code H-31

Step 1: Visual Inspection Locate the pump torque control solenoid on the main hydraulic pump (left side of engine). Inspect the wiring harness for abrasion, particularly where it routes along the pump body. Check the electrical connector for corrosion, bent pins, or oil contamination—common issues on used excavators.

Step 2: Electrical Testing Using a digital multimeter, check solenoid resistance (should read 18-22 ohms at 68°F). Test for voltage supply at the connector with ignition on (should show 12V). Check ground circuit continuity to the ECM—resistance above 1 ohm indicates harness issues.

Step 3: Functional Testing Connect Komatsu KOMTRAX Plus diagnostic software to monitor real-time solenoid command values versus actual response. Perform an ECM output test to activate the solenoid while monitoring amperage draw (normal: 0.6-0.8A). High current indicates internal short; no current suggests open circuit.

Step 4: Component Replacement If electrical values are correct but code persists, replace the torque control solenoid valve (Part #: 702-21-55901). For used machines, simultaneously replace the connector pigtail to eliminate corrosion issues. Clear codes and perform load testing with combined hydraulic functions.

Disclaimer: This guide provides general diagnostic procedures. Always consult the official Komatsu PC240LC-10 service manual and consider professional evaluation for complex hydraulic system repairs, especially on used equipment where multiple degraded components may contribute to fault conditions.