Komatsu PC200-10 Fault Code H-6: Complete Diagnostic Guide

What is Komatsu PC200-10 Fault Code H-6?

Fault Code H-6 on the Komatsu PC200-10 excavator indicates a hydraulic oil temperature sensor malfunction or abnormally high hydraulic oil temperature exceeding system parameters (typically above 110°C/230°F). This code is triggered when the Electronic Control Module (ECM) detects either a sensor circuit fault or legitimately dangerous temperature levels in the hydraulic system.

The hydraulic oil temperature sensor monitors the critical thermal condition of the PC200-10's hydraulic fluid, which directly affects viscosity, component lubrication, and seal integrity. When temperatures exceed safe operating limits, the hydraulic pump, control valves, and cylinder seals face accelerated wear. This monitoring system is essential for preventing catastrophic hydraulic component failure and maintaining optimal machine performance in demanding excavation applications.

Common Symptoms

When Code H-6 is active, operators typically experience:

• Hydraulic oil temperature warning light illuminated on the instrument cluster (red or amber)
• Reduced machine performance with slower cycle times and decreased digging force as the system enters derate mode
• Audible warning alarm from the cab monitoring system
• Noticeably hot hydraulic tank to the touch during inspections
• Possible sluggish hydraulic response during operation, particularly in bucket and boom movements

Potential Causes

The most common technical causes for H-6 code activation on used PC200-10 excavators include:

• Faulty hydraulic oil temperature sensor (resistance values outside specification range of 200-400 ohms at operating temperature)
• Damaged sensor wiring harness due to chafing against the tank mounting bracket—a known wear point on this model
• Corroded or loose electrical connector at the sensor terminal, allowing moisture infiltration
• Genuinely overheated hydraulic oil caused by blocked oil cooler fins, failed cooling fan, or low hydraulic oil level
• Malfunctioning thermostat in the hydraulic cooling circuit preventing proper temperature regulation
• ECM software calibration issues in machines with updated controller firmware

How to Troubleshoot and Fix Code H-6

Step 1: Visual Inspection Check the hydraulic oil level using the sight glass—low fluid causes excessive heat generation. Inspect the oil cooler for debris blockage and clean fins thoroughly with compressed air. On used excavators, examine the sensor wiring harness routing near the hydraulic tank for visible wear, particularly where it contacts metal surfaces.

Step 2: Sensor Circuit Testing Using a digital multimeter, disconnect the temperature sensor connector and measure resistance across the sensor terminals. At room temperature (20°C/68°F), resistance should read approximately 2,000-2,500 ohms; at operating temperature (80°C/176°F), expect 200-400 ohms. Values outside this range indicate sensor failure requiring replacement (Komatsu part #6732-81-3140).

Step 3: Wiring and Connector Verification Inspect the sensor connector for corrosion, bent pins, or moisture—common issues in older machines. Check wiring continuity from sensor to ECM pin 42 using your multimeter's continuity function. Test for voltage supply (should be 5V reference) from the ECM with ignition on.

Step 4: Actual Temperature Verification Use an infrared thermometer to measure actual hydraulic oil temperature at the tank. If the physical temperature exceeds 95°C (203°F) but the sensor reads normally, investigate cooling system components: verify hydraulic fan operation, check thermostat function, and ensure proper coolant circulation.

Step 5: Advanced Diagnostics Connect Komatsu KOMTRAX or compatible diagnostic software to monitor live sensor data and verify ECM programming. Clear codes after repairs and perform a functional test cycle under load.

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Disclaimer: This guide provides general diagnostic information. Hydraulic systems operate under extreme pressure and temperature. Always consult the Komatsu PC200-10 Service Manual and consider professional technician assistance for complex repairs, especially on used equipment with unknown service history.