Komatsu PC750LC-7 Fault Code H-6: Complete Diagnostic Guide

What is Komatsu PC750LC-7 Fault Code H-6?

Fault Code H-6 indicates a hydraulic oil temperature sensor circuit malfunction in the Komatsu PC750LC-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 PC750LC-7 because the hydraulic system relies on accurate temperature monitoring to prevent overheating and maintain optimal viscosity. The ECM uses this data to regulate hydraulic pump output, activate cooling fans, and protect expensive hydraulic components from thermal damage. Ignoring this code can lead to reduced machine performance, accelerated component wear, and potential catastrophic hydraulic system failure.

Common Symptoms

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

• Hydraulic oil temperature warning light illuminated on the monitor panel
• Reduced hydraulic performance or sluggish operation, especially during warm-up
• Cooling fan running continuously at high speed regardless of actual oil temperature
• Machine derate mode limiting engine RPM and hydraulic flow to protect the system
• Inaccurate temperature readings displayed on the monitor (showing extremely high or low values)

Potential Causes

The most common technical reasons for H-6 fault code on used PC750LC-7 excavators include:

• Failed hydraulic oil temperature sensor due to age, thermal cycling, or internal element degradation
• Damaged or corroded wiring harness at known rub points near the hydraulic tank mounting brackets
• Loose or corroded electrical connectors at the sensor or ECM interface
• Broken or chafed sensor wires caused by vibration and movement in the engine compartment
• ECM internal circuit failure (rare, but possible in high-hour machines)
• Contaminated sensor tip from debris or sludge buildup in older hydraulic oil

How to Troubleshoot and Fix Code H-6

Step 1: Visual Inspection Begin by locating the hydraulic oil temperature sensor (typically mounted in the hydraulic tank or return line). Inspect the wiring harness from sensor to ECM for obvious damage, chafing, or corrosion. On used excavators, pay special attention to harness routing near moving components and sharp edges where insulation wear commonly occurs.

Step 2: Electrical Testing Using a digital multimeter, disconnect the sensor connector and measure resistance across the sensor terminals. At room temperature (20°C), resistance should typically read 2,000-3,000 ohms (consult your service manual for exact specifications). Check for continuity in the wiring harness and verify ground integrity. Measure voltage supply at the sensor connector with ignition on—should read approximately 5 volts.

Step 3: Sensor and Connector Service Clean all electrical connectors with contact cleaner and inspect pins for corrosion or bent terminals. If resistance values are out of specification or the sensor shows physical damage, replace the temperature sensor with a genuine Komatsu part. For used machines, consider replacing the connector pigtail if corrosion is present, as this prevents recurring failures.

Step 4: System Verification Clear the fault code using Komatsu diagnostic software (KOMTRAX) or a compatible scan tool. Operate the machine through a complete warm-up cycle while monitoring live temperature data. Verify the sensor reads progressively increasing temperatures and that the cooling fan activates at the proper threshold.

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Disclaimer: This guide provides general diagnostic information. Always consult the official Komatsu PC750LC-7 service manual and consider professional assistance from certified Komatsu technicians for complex repairs or if you're unfamiliar with hydraulic system diagnostics.