Komatsu PC200-8E0 Fault Code H-6: Complete Diagnostic Guide

What is Komatsu PC200-8E0 Fault Code H-6?

Fault Code H-6 on the Komatsu PC200-8E0 indicates a hydraulic oil temperature sensor abnormality or excessively high hydraulic oil temperature. This code specifically monitors the hydraulic system temperature through the temperature sensor located in the main hydraulic circuit, typically near the hydraulic oil cooler or tank.

This fault is critical for the PC200-8E0's performance because excessive hydraulic oil temperature degrades fluid viscosity, reduces lubrication efficiency, and can cause seal degradation, pump cavitation, and accelerated component wear. The machine's Electronic Control Module (ECM) monitors this temperature continuously to prevent catastrophic hydraulic system damage. When activated, the system may automatically reduce engine RPM or hydraulic flow to protect components.

Common Symptoms

• Hydraulic oil temperature warning light illuminated on the instrument cluster (red or amber)
• Noticeable reduction in hydraulic power or slower cycle times for boom, arm, and bucket operations
• Automatic engine derate where maximum RPM is limited to approximately 1500-1800 RPM
• Audible warning alarm sounding intermittently or continuously from the cab
• Visible steam or excessive heat radiating from the hydraulic oil cooler or tank area

Potential Causes

On used Komatsu PC200-8E0 excavators, H-6 commonly results from:

• Hydraulic oil temperature sensor failure – common after 8,000+ operating hours due to thermal cycling and exposure to contaminants
• Plugged or restricted hydraulic oil cooler – debris buildup between cooling fins reduces heat dissipation efficiency
• Damaged or corroded sensor wiring harness – particularly at connection points near the engine where vibration and heat cause insulation breakdown
• Low hydraulic oil level or contaminated hydraulic oil reducing thermal transfer properties
• Faulty hydraulic cooling fan or thermostatic valve preventing adequate oil cooling
• ECM calibration issues or incorrect sensor resistance values stored after previous repairs

How to Troubleshoot and Fix Code H-6

Step 1: Initial Visual Inspection Check actual hydraulic oil temperature using an infrared thermometer at the tank (normal operating temperature: 60-80°C / 140-176°F). Inspect the hydraulic oil cooler for external blockage, bent fins, or debris accumulation. Verify hydraulic oil level meets specification and oil condition (check for discoloration, burnt smell, or contamination).

Step 2: Sensor and Wiring Diagnostics Locate the hydraulic oil temperature sensor (typically mounted on the hydraulic tank or main valve body). Disconnect the sensor connector and inspect for corrosion, oil contamination, or damaged pins—common issues in used machines. Using a digital multimeter, measure sensor resistance at ambient temperature (typical specification: 2-3 kΩ at 20°C). Compare readings against Komatsu's resistance-temperature chart in the service manual.

Step 3: Circuit and ECM Testing With the sensor disconnected, measure voltage supply from the ECM harness (should read approximately 5V reference voltage). Check for continuity and resistance in the sensor signal wire back to the ECM—any reading above 5Ω indicates harness damage. On used excavators, physically trace the harness for rubbing points against the chassis, particularly near rotating components or areas with excessive heat exposure.

Step 4: Component Replacement and System Verification If sensor resistance is out of specification or wiring shows damage, replace the temperature sensor (Komatsu part number specific to PC200-8E0) and repair harness sections with heat-resistant, oil-resistant wiring. After replacement, clear codes using Komatsu diagnostic software (KOMTRAX) or a compatible diagnostic tool, and monitor temperature readings during a 30-minute operational test under normal load conditions.

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Disclaimer: This guide provides general diagnostic procedures. Always consult the official Komatsu PC200-8E0 service manual and consider professional heavy equipment technician assistance for complex repairs, especially concerning ECM programming or hydraulic system overhauls.