What is Komatsu PC100-6 Fault Code H-27?

Fault Code H-27 on the Komatsu PC100-6 excavator indicates a hydraulic oil temperature sensor circuit malfunction. This code specifically relates to an abnormal voltage signal from the hydraulic oil temperature sensor to the machine's controller unit, typically caused by circuit issues, sensor failure, or temperature reading inconsistencies.

The hydraulic oil temperature monitoring system is critical for the PC100-6's operational safety and longevity. When hydraulic fluid exceeds safe operating temperatures (typically above 95-100°C), it degrades rapidly, losing viscosity and reducing the effectiveness of seals, pumps, and control valves. This code ensures the machine alerts operators before thermal damage occurs to expensive hydraulic components.

Common Symptoms

When Code H-27 is active, operators typically experience:

• Warning light illumination on the instrument cluster, often with a temperature symbol
• Intermittent or constant alarm buzzer depending on controller programming
• Incorrect temperature gauge readings showing unrealistic highs, lows, or erratic fluctuations
• Potential machine derate or reduced hydraulic responsiveness if the controller enters a protective mode
• Stored fault code in system memory even after temperature returns to normal

Potential Causes

The most common technical reasons for H-27 on used PC100-6 excavators include:

• Faulty hydraulic oil temperature sensor (resistance drift due to age or thermal cycling)
• Damaged wiring harness between sensor and controller, particularly at flex points near the hydraulic tank mounting
• Corroded or loose electrical connectors at the sensor or controller terminals (common in machines exposed to moisture)
• Broken or chafed sensor wires where the harness routes along the boom or near rotating components
• ECU/controller internal failure (less common, but possible in high-hour used machines)
• Poor ground connections causing voltage reference issues

How to Troubleshoot and Fix Code H-27

Step 1: Visual Inspection Begin by locating the hydraulic oil temperature sensor (typically mounted on the hydraulic tank or return line). Inspect the connector terminals for corrosion, oil contamination, or bent pins. On used excavators, check the wiring harness for visible damage, especially where it passes through high-wear areas or contact points with the frame.

Step 2: Electrical Testing Using a digital multimeter, disconnect the sensor and measure its resistance at ambient temperature (typically 2,000-3,000 ohms at 20°C for Komatsu sensors). Compare readings to the service manual specifications. Check continuity from sensor connector to the controller plug, and verify voltage supply (usually 5V reference from ECU) at the sensor connector with ignition on.

Step 3: Circuit and Ground Verification Test for short circuits between signal wire and ground, or signal wire and power supply. Verify the ground circuit integrity, as poor grounds are frequent culprits in older machines. If wiring checks pass but the sensor resistance is out of spec, replace the temperature sensor (part number 7861-93-1651 or equivalent).

Step 4: Component Replacement and Verification After replacing faulty components on used excavators, clear the fault code using Komatsu diagnostic software (KOMTRAX or equivalent scan tool) and monitor during operation. For persistent codes after sensor replacement, suspect ECU issues or internal controller damage.

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Disclaimer: This guide provides general troubleshooting information. Always consult the official Komatsu service manual for your specific serial number and consult qualified diesel technicians for complex electrical diagnostics or warranty concerns.