Komatsu PC800SE-8R Fault Code H-5: Complete Diagnostic Guide

What is Komatsu PC800SE-8R Fault Code H-5?

Fault Code H-5 indicates a hydraulic oil temperature sensor circuit malfunction in the Komatsu PC800SE-8R excavator. This code triggers 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 failure.

The hydraulic oil temperature sensor plays a critical role in protecting the PC800SE-8R's hydraulic system by monitoring fluid temperature and preventing overheating damage. When this sensor fails, the ECM cannot accurately regulate hydraulic system performance, potentially leading to reduced efficiency, component wear, or catastrophic hydraulic failure. For a machine of this size and complexity, maintaining proper hydraulic temperature monitoring is essential for preventing costly downtime and extending component life.

Common Symptoms

When Code H-5 is active, operators typically experience:

• Warning light illuminated on the monitor panel with hydraulic system alert
• Hydraulic system derate or reduced performance to prevent potential overheating
• Inaccurate or erratic hydraulic oil temperature readings on the display
• Machine may enter limp mode limiting operational capabilities
• Intermittent loss of hydraulic power during extended operation cycles

Potential Causes

The most common technical causes for Code H-5 in used PC800SE-8R excavators include:

• Hydraulic oil temperature sensor failure due to age, heat cycling, or internal component degradation
• Damaged wiring harness at known rub points near the hydraulic tank or along the main boom
• Corroded or loose connector pins at the sensor connection point (common in machines with high operating hours)
• ECM internal circuit failure affecting the sensor input channel
• Contaminated sensor threads causing poor ground connection or thermal transfer issues
• Previous repair attempts using non-OEM sensors with incorrect resistance specifications

How to Troubleshoot and Fix Code H-5

Step 1: Visual Inspection Begin by locating the hydraulic oil temperature sensor (typically mounted on the hydraulic tank). Inspect the wiring harness for obvious damage, chafing, or oil contamination. Check the connector for corrosion, bent pins, or moisture intrusion—common issues in used excavators operating in harsh environments.

Step 2: Electrical Testing Disconnect the sensor connector and use a digital multimeter to measure sensor resistance. At room temperature (20°C/68°F), resistance should typically read between 2,000-3,000 ohms (consult your service manual for exact specifications). Test harness continuity from the sensor connector back to the ECM pins, checking for opens or shorts to ground.

Step 3: Voltage Signal Verification With the ignition on and sensor disconnected, measure the supply voltage at the harness connector—should read approximately 5 volts. If voltage is absent or incorrect, trace the circuit toward the ECM for wiring faults or check for ECM power supply issues.

Step 4: Component Replacement If the sensor tests outside specifications, replace it with a genuine Komatsu OEM sensor to ensure proper resistance curves. For used excavators, always apply anti-seize compound to sensor threads and use a new sealing washer. After replacement, clear codes using Komatsu diagnostic software (KOMTRAX) and perform a functional test under operating temperature.

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 ECM repairs.