Komatsu PC800SE-7 Fault Code H-6: Complete Diagnostic Guide

What is Komatsu PC800SE-7 Fault Code H-6?

Fault Code H-6 indicates a hydraulic oil temperature sensor circuit malfunction in the Komatsu PC800SE-7 excavator. This code is triggered when the Electronic Control Module (ECM) detects an abnormal voltage signal from the hydraulic oil temperature sensor, typically indicating an open circuit, short circuit, or sensor reading outside the normal operating range (usually -40°C to 150°C).

This fault is critical for the PC800SE-7's performance because the hydraulic system relies on accurate temperature monitoring to prevent overheating, maintain optimal viscosity, and protect expensive hydraulic components. When this sensor fails, the machine may enter a protective derate mode or display inaccurate temperature readings, potentially leading to catastrophic hydraulic system damage if ignored.

Common Symptoms

• Hydraulic oil temperature warning light illuminated on the operator display panel
• Machine derate or reduced hydraulic power as the ECM enters protective mode
• Inaccurate or frozen temperature readings on the monitor (showing -40°C or maximum values)
• Intermittent fault code that appears and disappears, especially during cold starts or heavy operation
• Audible warning alarms in the cab when the code becomes active

Potential Causes

The most common technical causes for H-6 on used PC800SE-7 excavators include:

• Damaged or corroded sensor connector at the hydraulic tank, often caused by moisture intrusion or age-related deterioration
• Failed hydraulic oil temperature sensor (NTC thermistor type) due to internal element breakdown
• Wiring harness damage between the sensor and ECM, particularly at known rub points near the hydraulic tank mounting bracket
• Broken or frayed wires in the sensor circuit caused by vibration stress over thousands of operating hours
• ECM internal fault (rare) affecting the temperature sensor input circuit
• Poor ground connection at the sensor or ECM mounting points due to corrosion

How to Troubleshoot and Fix Code H-6

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. On used excavators, check the wiring harness for chafing, especially where it routes near moving components or sharp edges.

Step 2: Electrical Testing Using a digital multimeter, disconnect the sensor and measure its resistance at ambient temperature (should read approximately 2,000-3,000 ohms at 20°C for typical NTC sensors). Check for continuity in the wiring between the sensor connector and the ECM. Measure voltage supply from the ECM (typically 5V reference voltage) with the ignition on.

Step 3: Component Replacement and Verification If resistance values are out of specification or wiring shows damage, replace the faulty component. For used machines, always clean connector terminals with electrical contact cleaner and apply dielectric grease before reconnection. Clear the fault code using Komatsu diagnostic software (KOMTRAX) or a compatible scan tool, then operate the machine through a full temperature cycle to verify the repair.

Disclaimer: This guide provides general diagnostic information. Always consult the official Komatsu service manual for your specific serial number and consider professional assistance for complex electrical diagnostics or if you're unfamiliar with high-voltage systems.