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

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

Fault Code H-8 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 reading outside the normal operating range (usually -40°C to 150°C).

This fault is critical for the PC800SE-8R because hydraulic oil temperature directly affects system viscosity, component protection, and overall machine performance. The ECM uses this data to prevent overheating damage to expensive hydraulic pumps, motors, and cylinders. When this sensor fails, the machine may enter a protective derate mode or display inaccurate temperature readings, potentially leading to catastrophic hydraulic system failure 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 constant maximum or minimum values)
• Intermittent fault code that appears and disappears, especially during cold starts or high-load operations
• Audible warning alarms in the cab when hydraulic temperature thresholds are supposedly exceeded

Potential Causes

• Failed hydraulic oil temperature sensor due to internal element degradation (common in machines with 5,000+ hours)
• Damaged or corroded wiring harness at connector points, particularly where the harness routes near the hydraulic tank
• Chafed wires from rubbing against the tank mounting bracket or frame—a known wear point on PC800 series excavators
• Corroded connector pins at the sensor plug due to moisture intrusion or hydraulic oil contamination
• ECM internal fault (rare, but possible in used machines with electrical system history)
• Poor ground connection at the sensor mounting point or main chassis ground

How to Troubleshoot and Fix Code H-8

Step 1: Visual Inspection Begin by locating the hydraulic oil temperature sensor on the hydraulic tank (typically mounted on the side or return line). Inspect the wiring harness for obvious damage, chafing, or oil contamination. Check the connector for corrosion, bent pins, or moisture. On used excavators, pay special attention to harness routing near moving components or sharp edges.

Step 2: Electrical Testing Using a digital multimeter, disconnect the sensor and measure resistance across the sensor terminals. Compare readings against Komatsu specifications (typically 200-400 ohms at 20°C, varying with temperature). Check for continuity in the wiring from sensor to ECM. Measure voltage supply at the connector (should be approximately 5V reference voltage from ECM).

Step 3: Component Replacement and Verification If the sensor tests faulty, replace it with a genuine Komatsu part or OEM-equivalent sensor. Clean all connector pins with electrical contact cleaner and apply dielectric grease to prevent future corrosion. After replacement, clear the fault code using Komatsu diagnostic software (KOMTRAX) or a compatible scan tool, then operate the machine through a full heat cycle to verify the repair.

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