Komatsu PC800LC-8R Fault Code H-20: Complete Diagnostic Guide

What is Komatsu PC800LC-8R Fault Code H-20?

Fault Code H-20 indicates a hydraulic oil temperature sensor circuit malfunction in the Komatsu PC800LC-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 PC800LC-8R's hydraulic system from overheating damage. When functioning properly, it allows the ECM to implement protective measures—such as reducing engine RPM or limiting hydraulic flow—when oil temperatures exceed safe operating thresholds. For a large excavator like the PC800LC-8R, maintaining optimal hydraulic oil temperature (typically 50-80°C) is essential for preserving seal integrity, preventing component wear, and ensuring consistent hydraulic performance under heavy loads.

Common Symptoms

When Code H-20 is active, operators typically experience:

• Warning light illuminated on the monitor panel, often accompanied by a hydraulic system alert
• Inaccurate temperature readings displayed on the instrument cluster (showing extremely high, low, or erratic values)
• Reduced machine performance if the ECM enters a protective derate mode due to perceived overheating
• Intermittent code activation during machine operation, particularly when traveling over rough terrain
• Hydraulic system operating normally despite the fault code (indicating sensor issue rather than actual overheating)

Potential Causes

The most common technical causes for H-20 in used PC800LC-8R excavators include:

• Faulty hydraulic oil temperature sensor due to internal element degradation or contamination exposure
• Damaged wiring harness near the hydraulic tank area, where cables experience vibration and potential abrasion against frame components
• Corroded or loose electrical connectors at the sensor or ECM connection points (common in machines exposed to moisture)
• Open or short circuit in the sensor signal wire between the sensor and ECM
• ECM internal fault (rare, but possible in high-hour machines with electrical system history)
• Contaminated hydraulic oil causing sensor element fouling or coating

How to Troubleshoot and Fix Code H-20

Step 1: Visual Inspection Begin by locating the hydraulic oil temperature sensor (typically mounted on the hydraulic tank). Inspect the wiring harness from the sensor to the ECM for visible damage, chafing, or wear points. On used excavators, pay special attention to areas where harnesses route near moving components or sharp edges. Check all electrical connectors for corrosion, bent pins, or moisture intrusion.

Step 2: Electrical Testing Using a digital multimeter, disconnect the sensor and measure its resistance at various temperatures (refer to Komatsu specifications, typically 200-400 ohms at 20°C). Test the wiring continuity from the sensor connector to the ECM harness connector. Check for voltage supply from the ECM (usually 5V reference voltage) with the ignition on and sensor disconnected.

Step 3: Component Replacement and Verification If resistance values are out of specification or wiring shows faults, replace the defective component. For used machines, consider replacing both the sensor and connector simultaneously if corrosion is present, as connector resistance can cause intermittent faults. After repairs, clear the code using Komatsu diagnostic software (KOMTRAX) and monitor during operation to confirm the fix.

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