Komatsu PC800-8R Fault Code H-6: Complete Diagnostic Guide

What is Komatsu PC800-8R Fault Code H-6?

Fault Code H-6 on the Komatsu PC800-8R indicates a hydraulic oil temperature sensor circuit malfunction or abnormally high hydraulic oil temperature. This code is triggered when the Electronic Control Module (ECM) detects either an electrical fault in the temperature sensor circuit or when hydraulic oil temperature exceeds the manufacturer's safe operating threshold (typically above 110-120°C).

This fault is critical for the PC800-8R because excessive hydraulic oil temperature can cause rapid degradation of seals, accelerated component wear, and reduced hydraulic system efficiency. The hydraulic temperature sensor monitors oil temperature in the main hydraulic tank and sends voltage signals to the ECM, which uses this data to protect the system from thermal damage.

Common Symptoms

When Code H-6 is active, operators typically experience:

• Warning light illuminated on the instrument panel, often accompanied by an audible alarm
• Automatic derate of engine power or hydraulic flow to prevent further temperature increase
• Sluggish hydraulic response or reduced cycle times due to protective mode activation
• Temperature gauge reading abnormally high or displaying erratic values
• In severe cases, automatic machine shutdown to prevent catastrophic hydraulic system damage

Potential Causes

The most common technical causes for Code H-6 on used PC800-8R excavators include:

• Faulty hydraulic oil temperature sensor – sensor element degradation is common in high-hour machines
• Damaged or corroded wiring harness connections at the sensor or ECM, particularly where harnesses route near hot engine components
• Actual hydraulic oil overheating due to clogged hydraulic oil cooler fins or failed cooling fan
• Low hydraulic oil level causing insufficient heat dissipation
• ECM internal fault or corrupted calibration data (less common)
• Worn hydraulic pump creating excessive heat through internal leakage
• Blocked hydraulic return filters increasing system backpressure and heat generation

How to Troubleshoot and Fix Code H-6

Step 1: Visual Inspection Begin by checking hydraulic oil level and condition. Inspect the hydraulic oil cooler for debris, bent fins, or blockage. Verify the cooling fan operates correctly. On used excavators, examine the sensor wiring harness for chafing, particularly where it passes near the hydraulic tank and engine block.

Step 2: Sensor Circuit Testing Using a digital multimeter, disconnect the temperature sensor connector and measure resistance across the sensor terminals. At 25°C, resistance should typically read 2,000-3,000 ohms (consult service manual for exact specifications). Check for voltage supply at the harness connector (usually 5V reference voltage from ECM).

Step 3: Connector and Harness Verification Inspect connector pins for corrosion, bent terminals, or moisture intrusion—common issues in used machines. Check continuity between the sensor connector and ECM pins to identify broken wires. Measure insulation resistance to ground (should exceed 10 megohms).

Step 4: Component Replacement If sensor resistance is out of specification or circuit testing reveals faults, replace the hydraulic temperature sensor using genuine Komatsu parts. Clear the fault code using Komatsu diagnostic software (KOMTRAX) or a compatible scan tool and monitor for recurrence.

Step 5: Address Root Causes If the sensor tests correctly but actual oil temperature is high, service the hydraulic system: clean the oil cooler, replace hydraulic filters, and verify proper oil viscosity for operating conditions.

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Disclaimer: This guide provides general diagnostic information. Always consult the official Komatsu PC800-8R service manual and consider professional assistance from certified Komatsu technicians for complex repairs, especially on high-value used equipment.