What is Komatsu PC110-8M0 Fault Code H-6?

Fault Code H-6 on the Komatsu PC110-8M0 indicates a hydraulic oil temperature sensor malfunction or abnormally high hydraulic oil temperature. This diagnostic trouble code (DTC) is triggered when the machine's electronic control module (ECM) detects either a sensor circuit failure or that hydraulic oil temperature has exceeded the safe operating threshold (typically above 110°C/230°F).

This code is critical for the PC110-8M0 because excessive hydraulic oil temperature directly impacts the excavator's hydraulic system efficiency, seal integrity, and component longevity. The hydraulic oil temperature sensor monitors fluid conditions to prevent catastrophic pump failure, cylinder seal damage, and accelerated oil degradation. In used excavators, this sensor and its wiring harness are particularly vulnerable to heat cycling, vibration damage, and corrosion—making H-6 a relatively common fault in older machines.

Common Symptoms

When fault code H-6 is active, operators typically experience:

• Hydraulic oil temperature warning lamp illuminated on the instrument cluster (amber or red depending on severity)
• Reduced hydraulic response or sluggish boom, arm, and bucket movement as the system enters protective derate mode
• Audible warning alarm from the cab monitoring system
• Visible overheating of hydraulic components or unusual heat radiating from the hydraulic tank
• Intermittent code activation during heavy workload cycles or high ambient temperature conditions

Potential Causes

The most common technical causes for H-6 on used PC110-8M0 excavators include:

• Faulty hydraulic oil temperature sensor (sensor element failure or internal short circuit)
• Damaged sensor wiring harness at known rub points near the hydraulic tank mounting bracket or engine bay
• Corroded or loose electrical connectors at the sensor connection point (common in machines exposed to moisture)
• Actual hydraulic system overheating due to plugged hydraulic oil cooler, low coolant flow, or failed cooling fan
• Low hydraulic oil level causing inadequate heat dissipation and genuine temperature spikes
• Degraded hydraulic oil with wrong viscosity or contamination reducing thermal transfer properties

How to Troubleshoot and Fix Code H-6

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 sensor body, connector, and wiring harness for obvious damage, oil contamination, corrosion, or connector looseness. On used excavators, check for harness chafing against metal edges or heat sources—a common failure point on the PC110-8M0 due to engine vibration.

Step 2: Electrical Testing Disconnect the sensor connector and use a digital multimeter to measure sensor resistance. Compare readings against Komatsu specifications (typically 200-300 ohms at 20°C ambient). Test circuit continuity from the sensor connector back to the ECM using a wiring diagram. Check for short to ground or open circuits in the harness. Measure supply voltage from the ECM (should be approximately 5V reference).

Step 3: Verify Actual Temperature Use an infrared thermometer or temperature probe to measure actual hydraulic oil temperature at the tank. If oil temperature genuinely exceeds 100°C, inspect the hydraulic oil cooler for blockages, check cooling fan operation, verify hydraulic oil level, and test oil condition. If temperature is normal but code persists, replace the temperature sensor with a genuine Komatsu part.

Step 4: Check Hydraulic System Health For used machines, perform a comprehensive hydraulic system inspection: check oil filter condition, inspect for external leaks causing low oil level, verify proper oil viscosity (ISO VG 46 recommended), and examine the cooler core for debris accumulation. Clean or replace the cooler if flow is restricted.

Step 5: Clear Code and Test After repairs, use Komatsu diagnostic software (KOMTRAX or compatible scan tool) to clear stored fault codes. Operate the machine under normal load conditions while monitoring hydraulic oil temperature in real-time. Verify code does not return and temperature remains within normal range (70-90°C operating).

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Disclaimer: This guide provides general diagnostic information for Komatsu PC110-8M0 fault code H-6. Always consult the official Komatsu service manual for your specific machine serial number and seek professional assistance from certified Komatsu technicians for complex repairs. Improper diagnostics can lead to equipment damage or safety hazards.