Komatsu PC650LC-8R Fault Code H-5: Complete Diagnostic Guide

What is Komatsu PC650LC-8R Fault Code H-5?

Fault Code H-5 indicates a hydraulic oil temperature sensor circuit malfunction in the Komatsu PC650LC-8R excavator. This code triggers when the Electronic Control Module (ECM) detects an abnormal voltage signal from the hydraulic oil temperature sensor, which monitors the operating temperature of the hydraulic system fluid.

The hydraulic oil temperature sensor plays a critical role in protecting the PC650LC-8R's hydraulic system from overheating damage. When functioning properly, it allows the ECM to adjust pump output and activate warning systems before temperatures reach damaging levels. For used excavators operating in demanding conditions, this sensor becomes essential for preventing catastrophic hydraulic component failure and maintaining optimal system efficiency.

Common Symptoms

When Code H-5 is active, operators typically experience:

• Hydraulic oil temperature warning light illuminated on the monitor panel, even when oil feels cool to touch
• Intermittent or constant fault code display on the multi-information display
• Potential activation of derate mode, limiting engine RPM and hydraulic flow as a protective measure
• Inaccurate temperature readings showing extreme highs (over 120°C) or lows (below -40°C)
• Possible activation of audible warning alarms during normal operation

Potential Causes

The most common technical causes for Code H-5 in used PC650LC-8R excavators include:

• Hydraulic oil temperature sensor failure due to internal component degradation or contamination exposure
• Damaged or corroded wiring harness connections at the sensor plug, especially common near the hydraulic tank mounting area
• Open or short circuit in the sensor wiring caused by harness rubbing against frame components during boom/arm movement
• Corroded or loose ground connections affecting sensor signal integrity
• ECM internal fault (rare) causing improper voltage supply to the sensor circuit
• Contaminated hydraulic oil causing sensor element fouling in high-hour machines

How to Troubleshoot and Fix Code H-5

Step 1: Visual Inspection Begin by locating the hydraulic oil temperature sensor (typically mounted on the hydraulic tank). Inspect the sensor connector for corrosion, oil contamination, bent pins, or moisture intrusion. Check the wiring harness routing for visible damage, particularly where it passes near moving components or sharp edges—common wear points on used excavators.

Step 2: Electrical Testing Disconnect the sensor connector and use a digital multimeter to measure sensor resistance. At 20°C (68°F), resistance should typically read between 2,000-3,000 ohms (consult your service manual for exact specifications). Test harness continuity from the sensor connector back to the ECM pins, checking for opens or shorts to ground.

Step 3: Voltage Supply Check With the ignition on and sensor disconnected, measure the supply voltage at the harness connector. You should see approximately 5 volts from the ECM. If voltage is absent or incorrect, trace the circuit for damaged wires or check ECM power supply circuits.

Step 4: Component Replacement If the sensor tests outside specifications or harness damage is found, replace the faulty component using genuine Komatsu parts for reliability. For used excavators, always apply dielectric grease to connector pins during reassembly to prevent future corrosion. Clear codes using Komatsu diagnostic software (KOMTRAX) or a compatible scan tool and verify repair with a test cycle.

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Disclaimer: This guide provides general diagnostic information. Always consult the official Komatsu service manual for your specific machine serial number and consider professional assistance from certified Komatsu technicians for complex electrical diagnostics.