What is Komatsu PC100-6 Fault Code H-6?

Komatsu PC100-6 Fault Code H-6 indicates a hydraulic oil temperature sensor malfunction or abnormally high hydraulic oil temperature. This code is triggered when the engine control module (ECM) detects irregular voltage signals from the hydraulic oil temperature sensor or when oil temperature exceeds safe operating limits (typically above 110-120°C/230-248°F).

For the PC100-6 excavator, this fault is critical because excessive hydraulic oil temperature directly impacts system viscosity, seal integrity, and component longevity. The hydraulic system operates under high pressure, and overheating can cause catastrophic pump failure, cylinder seal damage, and accelerated fluid degradation. On used machines, this code often reveals underlying cooling system deterioration or sensor degradation from prolonged exposure to thermal cycling.

Common Symptoms

• Amber warning light illuminated on the instrument panel with reduced hydraulic performance
• Noticeable decrease in swing speed and boom/arm response time during operation
• Hydraulic oil appears darkened or has a burnt odor when checked
• Intermittent code appearance that becomes constant as the machine warms up
• Automatic derate or shutdown after 10-15 minutes of continuous operation

Potential Causes

• Hydraulic oil temperature sensor failure due to internal thermistor degradation (common in machines with 5,000+ hours)
• Corroded or damaged sensor connector from water intrusion at the tank mounting location
• Blocked or restricted hydraulic oil cooler fins clogged with debris, reducing heat dissipation
• Failed cooling fan motor or damaged fan blades preventing adequate airflow
• Rubbed or chafed sensor wiring harness where it passes near the swing motor housing
• Low hydraulic oil level causing inadequate circulation and heat buildup
• Degraded hydraulic oil with improper viscosity grade for operating conditions

How to Troubleshoot and Fix Code H-6

Step 1: Visual Inspection Check the hydraulic oil cooler for external blockage—remove debris from fins using compressed air. Inspect the cooling fan for proper rotation and blade damage. On used excavators, verify the fan belt tension and condition, as wear causes reduced airflow.

Step 2: Sensor and Wiring Verification Locate the hydraulic oil temperature sensor on the return line near the tank. Disconnect the two-wire connector and inspect for corrosion or moisture. Using a digital multimeter, measure sensor resistance—typical values range 200-300 Ω at 20°C (resistance decreases as temperature rises). Compare readings to Komatsu specifications.

Step 3: Circuit Testing With the sensor disconnected, check supply voltage at the harness connector (should read approximately 5V from the ECM). Inspect wiring for chafing points near frame rails and hydraulic hoses—a common failure area on PC100-6 models due to vibration wear.

Step 4: Hydraulic Oil Analysis Drain a sample and verify proper ISO VG 46 or VG 68 viscosity grade. Check oil level and condition; contaminated oil indicates component wear requiring system flushing.

Step 5: Component Replacement Replace the temperature sensor (Komatsu part number 7861-93-3320 or equivalent) if resistance values fall outside specifications. For persistent codes on used machines, replace the sensor-to-ECM harness section to eliminate intermittent connection issues.

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Disclaimer: This guide provides general diagnostic information. Always consult the Komatsu PC100-6 service manual and qualified diesel technicians for complex repairs. Improper diagnostics may cause additional equipment damage.