Komatsu PC800-8R Fault Code H-20: Complete Diagnostic Guide

What is Komatsu PC800-8R Fault Code H-20?

Fault Code H-20 indicates a hydraulic oil temperature sensor circuit malfunction in the Komatsu PC800-8R excavator. This code triggers when the Electronic Control Module (ECM) detects an abnormal voltage signal from the hydraulic oil temperature sensor, which monitors the operating temperature of the hydraulic system fluid.

The hydraulic oil temperature sensor plays a critical role in protecting the PC800-8R's hydraulic system from overheating damage. When functioning properly, it allows the ECM to adjust pump output and activate cooling systems as needed. On this 80-ton class excavator, maintaining optimal hydraulic temperatures (typically 50-80°C) is essential for preserving seal integrity, preventing fluid degradation, and ensuring consistent hydraulic performance across all functions.

Common Symptoms

When Code H-20 is active, operators typically experience:

• Warning light illuminated on the monitor panel with H-20 displayed
• Inaccurate or erratic hydraulic temperature readings on the dashboard display
• Hydraulic system derate or reduced performance as the ECM enters failsafe mode
• Cooling fan running continuously at high speed regardless of actual oil temperature
• Potential activation of overheat protection mode, limiting machine functions even when hydraulic oil is at normal temperature

Potential Causes

The most common technical causes for H-20 on used PC800-8R excavators include:

• Faulty hydraulic oil temperature sensor due to internal element failure or contamination exposure
• Damaged or corroded wiring harness connections at the sensor plug (common wear point near hydraulic tank)
• Open or short circuit in the sensor wiring between the sensor and ECM
• Corroded or loose connector pins at the sensor or ECM interface
• ECM internal fault affecting the temperature sensor input circuit (rare)
• Hydraulic oil contamination causing sensor element coating or failure

How to Troubleshoot and Fix Code H-20

Step 1: Visual Inspection Begin by locating the hydraulic oil temperature sensor on the hydraulic tank. Inspect the sensor connector and wiring harness for obvious damage, corrosion, oil contamination, or loose connections. On used excavators, check for harness chafing against the tank or frame—a known wear point on PC800 series machines.

Step 2: Electrical Testing Disconnect the sensor and use a digital multimeter to check sensor resistance. At 20°C, resistance should typically read 2,000-3,000 ohms (consult service manual for exact specifications). Test wiring continuity from the sensor connector to the ECM using the multimeter's continuity function. Check for short circuits to ground by measuring resistance between each wire and machine ground (should read infinite resistance).

Step 3: Voltage Signal Verification With the ignition on and sensor disconnected, measure supply voltage at the sensor connector (typically 5V reference voltage from ECM). If voltage is absent or incorrect, trace the harness for breaks or investigate potential ECM issues.

Step 4: Component Replacement If the sensor tests faulty, replace it with a genuine Komatsu temperature sensor. Clean all connector pins with electrical contact cleaner before reconnection. Clear the fault code using Komatsu diagnostic software (KOMTRAX) or a compatible scan tool, then test operate the machine to verify repair.

For used excavators, always inspect connector seals and apply dielectric grease to prevent future corrosion-related failures.

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Disclaimer: This guide provides general diagnostic information. Always consult the official Komatsu PC800-8R service manual and consider professional technician assistance for complex electrical diagnostics or repairs.