Komatsu PC800LC-8R Fault Code H-5: Complete Diagnostic Guide

What is Komatsu PC800LC-8R Fault Code H-5?

Fault Code H-5 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 machine of this size and complexity, maintaining proper hydraulic oil temperature is essential for preventing catastrophic component failure and ensuring optimal performance of all hydraulic functions.

Common Symptoms

When Code H-5 is active on your PC800LC-8R, operators typically experience:

• Hydraulic oil temperature warning light illuminated on the monitor panel
• Reduced machine performance or automatic derate mode activation, even when hydraulic oil temperature is normal
• Inaccurate or erratic hydraulic oil temperature readings displayed on the monitor
• Intermittent alarm activation during operation, particularly during temperature fluctuations
• Potential activation of backup mode, limiting swing speed and boom/arm functions

Potential Causes

The most common technical causes for Code H-5 in used PC800LC-8R excavators include:

• Faulty hydraulic oil temperature sensor due to age-related degradation or thermal cycling damage
• Damaged or corroded wiring harness connections at the sensor plug, especially from exposure to hydraulic fluid leaks
• Broken or chafed sensor wiring along known rub points near the hydraulic tank mounting area
• Corroded pins or moisture intrusion in the sensor connector (common in high-hour machines)
• ECM internal circuit failure (rare, but possible in older units)
• Poor ground connection at the sensor mounting point due to rust or paint buildup

How to Troubleshoot and Fix Code H-5

Step 1: Visual Inspection Begin by locating the hydraulic oil temperature sensor on the hydraulic tank (typically mounted on the side or bottom). Inspect the sensor connector for corrosion, oil contamination, bent pins, or moisture. Check the wiring harness from the sensor to the main harness for visible damage, chafing, or rub-through points—particularly where the harness passes near metal edges or moving components. On used excavators, this is often the primary failure point.

Step 2: Electrical Testing Using a digital multimeter, disconnect the sensor and measure its resistance at various temperatures (consult Komatsu specifications, typically 200-400 ohms at 20°C). Check for open circuits or short circuits in the wiring by measuring continuity from the sensor connector to the ECM pins. Verify supply voltage at the sensor connector (typically 5V reference voltage from the ECM). Inspect ground integrity by checking resistance between the sensor body and chassis ground (should be less than 1 ohm).

Step 3: Component Replacement and Verification If testing reveals sensor failure, replace the hydraulic oil temperature sensor with a genuine Komatsu part. Before installation, clean the mounting threads and apply anti-seize compound. If wiring damage is found, repair using heat-shrink solder connections and protect with additional split loom or conduit. After repairs, clear the fault code using Komatsu diagnostic software (KOMTRAX) or a compatible scan tool, then operate the machine through a full heat cycle to verify the repair.

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Disclaimer: This guide provides general diagnostic information for Code H-5. Always consult the official Komatsu PC800LC-8R service manual and consider professional assistance from certified Komatsu technicians for complex electrical diagnostics or if you're unfamiliar with high-voltage systems.