What is Komatsu PC110-8M0 Fault Code H-5?

Fault Code H-5 on the Komatsu PC110-8M0 excavator indicates a hydraulic oil temperature sensor circuit malfunction or an overheating condition in the hydraulic system. This diagnostic trouble code is triggered when the Engine Control Module (ECM) detects an abnormal signal from the hydraulic oil temperature sensor or when hydraulic fluid temperatures exceed safe operating thresholds (typically above 95-100°C/203-212°F).

The hydraulic oil temperature sensor plays a critical role in protecting the PC110-8M0's hydraulic system from thermal damage. When this code activates, the machine may enter a derate mode to prevent catastrophic component failure, including damage to hydraulic pumps, cylinders, and seals. For used excavators, this code often signals degraded cooling system performance or sensor deterioration common in machines with higher operating hours.

Common Symptoms

When Code H-5 is active on your Komatsu PC110-8M0, operators typically experience:

• Warning light illumination on the instrument cluster, specifically the hydraulic temperature indicator
• Reduced hydraulic response or sluggish boom, arm, and bucket movements as the system enters protection mode
• Audible alarm from the cabin warning system during operation
• Noticeable heat radiating from hydraulic oil cooler or tank areas
• Automatic engine derate limiting RPM to reduce hydraulic system load

Potential Causes

The most common technical causes for H-5 fault codes in used PC110-8M0 excavators include:

• Faulty hydraulic oil temperature sensor – Sensor element degradation or internal circuit failure (common after 5,000+ hours)
• Damaged wiring harness – Chafing at known rub points near the hydraulic tank mounting bracket or along the chassis rail
• Corroded electrical connectors – Moisture intrusion in the sensor connector causing intermittent signals
• Genuine hydraulic overheating – Blocked hydraulic oil cooler fins, low coolant levels, or failed cooling fan
• Contaminated hydraulic oil – Wrong viscosity or degraded fluid reducing heat dissipation efficiency
• ECM calibration issues – Outdated software parameters in older machines

How to Troubleshoot and Fix Code H-5

Step 1: Visual Inspection Begin by checking the hydraulic oil temperature sensor location (typically mounted on the hydraulic tank). Inspect the wiring harness for visible damage, particularly where it passes near moving components or sharp edges. Examine the electrical connector for corrosion, bent pins, or oil contamination—common issues in used excavators operating in harsh environments.

Step 2: Diagnostic Testing Using a digital multimeter, measure sensor resistance with the engine off. At ambient temperature (20°C/68°F), resistance should typically read 2,000-3,000 ohms (consult your specific service manual). Check for voltage supply at the sensor connector—should read approximately 5 volts with the key on. Use Komatsu KOMTRAX diagnostic software or a compatible scan tool to monitor live sensor data and compare readings to actual hydraulic oil temperature.

Step 3: Component Testing and Replacement If sensor readings are erratic or out of specification, replace the hydraulic oil temperature sensor with a genuine Komatsu part. Before installation, clean the mounting boss thoroughly and apply anti-seize compound. For used machines, verify the hydraulic oil cooler isn't blocked—remove debris from cooling fins and confirm cooling fan operation. Check hydraulic oil condition and level; replace if contaminated or incorrect viscosity.

Step 4: System Verification After repairs, clear fault codes using diagnostic software and operate the machine through a complete work cycle. Monitor hydraulic temperatures during high-load operations to ensure readings stay within normal range (typically 60-80°C/140-176°F during operation).

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Disclaimer: This guide provides general troubleshooting information for the Komatsu PC110-8M0. Always consult the official Komatsu service manual for your specific machine serial number and model year. If you're unfamiliar with hydraulic systems or electrical diagnostics, contact a certified Komatsu technician or qualified heavy equipment mechanic to prevent injury or further machine damage.