Komatsu PC70-8 Fault Code H-15: Complete Diagnostic Guide

What is Komatsu PC70-8 Fault Code H-15?

Fault Code H-15 on the Komatsu PC70-8 indicates a hydraulic oil temperature sensor circuit malfunction or abnormal temperature reading. This code is triggered when the Electronic Control Module (ECM) detects an out-of-range signal from the hydraulic oil temperature sensor, typically indicating an open circuit, short circuit, or sensor failure.

The hydraulic oil temperature sensor is critical for the PC70-8's performance management system. It monitors hydraulic fluid temperature to prevent overheating, optimize hydraulic pump efficiency, and protect system components. When this sensor fails, the ECM cannot properly regulate hydraulic system performance, potentially leading to reduced machine efficiency or component damage.

Common Symptoms

When Code H-15 is active, operators typically experience:

• Warning light illuminated on the instrument panel (hydraulic temperature indicator)
• Intermittent or constant alarm buzzer activation
• Reduced hydraulic system performance or derated power output
• Inaccurate hydraulic oil temperature readings on the display (showing abnormally high, low, or no reading)
• Potential activation of limp mode restricting machine operation in severe cases

Potential Causes

The most common technical causes for H-15 on used PC70-8 excavators include:

• Hydraulic oil temperature sensor failure due to age, heat exposure, or internal component degradation
• Wiring harness damage at known rub points near the hydraulic tank or along the chassis frame
• Corroded or loose connector pins at the sensor connection point (common in machines exposed to moisture)
• Open or short circuit in the sensor wiring between the sensor and ECM
• ECM internal fault (rare, but possible in high-hour machines)
• Contaminated hydraulic oil causing sensor element fouling

How to Troubleshoot and Fix Code H-15

Step 1: Visual Inspection Begin by locating the hydraulic oil temperature sensor (typically mounted on or near the hydraulic tank). Inspect the sensor connector for corrosion, bent pins, or moisture intrusion. On used excavators, check the wiring harness for chafing, especially where it routes near moving components or sharp edges.

Step 2: Electrical Testing Disconnect the sensor connector and use a digital multimeter to measure sensor resistance. Compare readings against Komatsu specifications (typically 200-400 ohms at room temperature). Check for continuity in the wiring harness from sensor to ECM. Test for voltage supply (usually 5V reference) at the connector with ignition on.

Step 3: Component Replacement and Verification If sensor resistance is out of specification or wiring shows damage, replace the faulty component. For used machines, always apply dielectric grease to connectors to prevent future corrosion. Clear the fault code using Komatsu diagnostic software (KOMTRAX or compatible scan tool) and monitor for recurrence during operation.

Disclaimer: This guide provides general diagnostic information. Always consult the official Komatsu service manual for your specific machine serial number and consider professional technician assistance for complex electrical diagnostics.