Komatsu PC110-7 Fault Code H-8: Complete Diagnostic Guide

What is Komatsu PC110-7 Fault Code H-8?

Fault Code H-8 on the Komatsu PC110-7 indicates a Hydraulic Oil Temperature Sensor malfunction or abnormally high hydraulic oil temperature. This code signals that the ECM (Engine Control Module) has detected either an out-of-range voltage signal from the hydraulic oil temperature sensor or that the hydraulic system temperature has exceeded safe operating limits (typically above 95-100°C or 203-212°F).

This fault is critical for the PC110-7 because excessive hydraulic temperatures can cause rapid degradation of hydraulic seals, reduce oil viscosity, and lead to catastrophic pump or motor failures. The excavator's performance depends on maintaining optimal hydraulic oil temperature for efficient operation and component longevity.

Common Symptoms

When Code H-8 is active, operators typically experience:

• Hydraulic oil temperature warning light illuminated on the instrument panel (red or amber)
• Reduced hydraulic response or sluggish movement of boom, arm, or bucket functions
• Automatic machine derate or shutdown in severe cases to protect hydraulic components
• Audible warning alarm sounding intermittently or continuously
• Visible steam or unusual odors from the hydraulic tank or cooler area in extreme overheat conditions

Potential Causes

The most common technical causes for H-8 on used PC110-7 excavators include:

• Faulty hydraulic oil temperature sensor due to age-related drift or internal failure
• Damaged or corroded wiring harness at sensor connector (common rub point near hydraulic tank)
• Clogged hydraulic oil cooler fins restricting airflow and preventing heat dissipation
• Low hydraulic oil level causing insufficient fluid circulation and heat buildup
• Failed cooling fan or malfunctioning fan motor relay reducing cooler efficiency
• Excessive hydraulic system load from worn pumps, cylinders, or relief valves generating excess heat
• Contaminated hydraulic oil with incorrect viscosity for ambient conditions

How to Troubleshoot and Fix Code H-8

Step 1: Visual Inspection Check hydraulic oil level using the dipstick (engine off, machine level). Inspect the hydraulic oil cooler for debris, bent fins, or blockages. On used excavators, examine the wiring harness routing from the temperature sensor to the ECM for abrasion points, particularly where it passes near the hydraulic tank mounting bracket.

Step 2: Sensor and Circuit Testing Locate the hydraulic oil temperature sensor (typically mounted on the hydraulic tank side). Disconnect the sensor connector and inspect for corrosion or oil contamination on pins. Using a digital multimeter, measure sensor resistance: it should read approximately 200-300 ohms at 20°C (68°F) and decrease as temperature rises. Check circuit continuity from sensor connector to ECM pin (consult service manual for specific pin location). Resistance should be less than 5 ohms; infinite resistance indicates an open circuit in the harness.

Step 3: Cooling System Verification Start the machine and observe cooling fan operation during warm-up. The fan should engage automatically as hydraulic temperature rises. Check fan motor voltage (should read 24V DC when activated). For used machines, verify the fan motor bearings aren't seized or worn. Clean the cooler thoroughly with compressed air or low-pressure water.

Step 4: Oil Quality and System Load Sample and inspect hydraulic oil condition—dark, burnt-smelling oil indicates overheating issues or contamination. Test system pressure at the main relief valve; excessive pressure (above 345 bar/5,000 psi) suggests relief valve problems causing heat generation. On high-hour used excavators, consider worn hydraulic pump efficiency as a heat source.

Professional Consultation Disclaimer: While these procedures assist in diagnosing Code H-8, complex hydraulic or electrical issues may require factory diagnostic software (Komatsu KOMTRAX or PC-based tools) and trained technician expertise. Always follow manufacturer service manual specifications for your specific machine serial number.