Komatsu PC850SE-8R Fault Code H-6: Complete Diagnostic Guide

What is Komatsu PC850SE-8R Fault Code H-6?

Fault Code H-6 indicates a hydraulic oil temperature sensor circuit malfunction or abnormally high hydraulic oil temperature in the Komatsu PC850SE-8R excavator. 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 or 230-248°F).

This fault is critical for the PC850SE-8R because excessive hydraulic oil temperature can cause rapid degradation of seals, reduced hydraulic efficiency, and potential damage to expensive hydraulic components including pumps, motors, and control valves. The hydraulic system is the lifeblood of excavator operation, making this code a priority concern.

Common Symptoms

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

• Warning light illuminated on the monitor panel, often accompanied by an audible alarm
• Reduced machine performance or automatic derate mode limiting hydraulic functions
• Visible overheating of hydraulic components or abnormally hot hydraulic oil tank
• Sluggish hydraulic response during operation, particularly in boom and bucket functions
• Monitor display showing elevated hydraulic oil temperature readings (if equipped with digital readout)

Potential Causes

The most common technical causes for Code H-6 in used PC850SE-8R excavators include:

• Faulty hydraulic oil temperature sensor due to age-related failure or contamination
• Damaged wiring harness or corroded connectors between the sensor and ECM (common wear point near the hydraulic tank)
• Actual hydraulic oil overheating caused by clogged hydraulic oil cooler, low coolant levels, or malfunctioning cooling fan
• Restricted hydraulic return filters causing excessive system pressure and heat generation
• ECM calibration issues or internal ECM faults (less common but possible in high-hour machines)
• Low hydraulic oil level reducing heat dissipation capacity

How to Troubleshoot and Fix Code H-6

Step 1: Visual Inspection Begin by checking the actual hydraulic oil temperature using an infrared thermometer at the tank. Compare this to the monitor reading. Inspect the hydraulic oil temperature sensor (typically located on or near the hydraulic tank) for physical damage, oil contamination on the connector, or corrosion. On used excavators, carefully examine the wiring harness routing for rub points, particularly where it passes near moving components or sharp edges.

Step 2: Electrical Testing Using a digital multimeter, disconnect the temperature sensor connector and measure resistance across the sensor terminals. Compare readings against Komatsu specifications (typically 200-400 ohms at 20°C, decreasing as temperature rises). Check for continuity in the wiring harness from sensor to ECM. Measure voltage supply at the sensor connector (should be approximately 5V reference voltage from ECM).

Step 3: System Verification If electrical tests pass, inspect the hydraulic oil cooler for blockages, debris, or fin damage. Verify cooling fan operation and check hydraulic oil level. Replace hydraulic return filters if service intervals have been exceeded. For persistent codes after sensor replacement, use Komatsu diagnostic software (KOMTRAX) to verify ECM functionality and check for software updates.

Critical for Used Equipment: Before replacing the temperature sensor, thoroughly clean all connector pins with electrical contact cleaner and apply dielectric grease. Many H-6 codes on older machines resolve with proper connector maintenance rather than parts replacement.

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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 seek qualified professional assistance for complex repairs or safety-critical systems.