Komatsu PC800-8R Fault Code H-5: Complete Diagnostic Guide

What is Komatsu PC800-8R Fault Code H-5?

Fault Code H-5 on the Komatsu PC800-8R indicates a hydraulic oil temperature sensor circuit malfunction or abnormally high hydraulic oil temperature. This code is triggered when the machine's Electronic Control Module (ECM) detects either an out-of-range signal from the hydraulic oil temperature sensor or when actual oil temperatures exceed safe operating thresholds (typically above 110-120°C).

This fault is critical for the PC800-8R because excessive hydraulic oil temperature can cause rapid degradation of seals, accelerated oil breakdown, and potential damage to hydraulic pumps and motors. The machine's monitoring system uses this sensor data to protect expensive hydraulic components and maintain optimal viscosity for system performance.

Common Symptoms

When Code H-5 is active, operators typically experience:

• Hydraulic oil temperature warning light illuminated on the monitor panel
• Audible alarm sounding in the cab during operation
• Reduced machine performance or automatic derate mode limiting hydraulic flow
• Sluggish hydraulic response in boom, arm, or swing functions
• Error message displayed on the multi-function monitor indicating high temperature or sensor fault

Potential Causes

The most common technical causes for H-5 on used PC800-8R excavators include:

• Failed hydraulic oil temperature sensor due to age-related degradation or thermal cycling damage
• Damaged wiring harness or corroded connectors between the sensor and ECM (common near the hydraulic tank mounting area)
• Actual hydraulic oil overheating caused by clogged hydraulic oil cooler, failed cooling fan, or restricted airflow
• Faulty hydraulic cooling fan motor or temperature-controlled fan clutch malfunction
• Low hydraulic oil level causing insufficient heat dissipation
• ECM calibration issues or software glitches in older machines

How to Troubleshoot and Fix Code H-5

Step 1: Visual Inspection Begin by checking the hydraulic oil level using the sight glass. Inspect the hydraulic oil cooler for debris, mud buildup, or damaged fins. On used excavators, examine the wiring harness routing near the hydraulic tank for chafing, cracking, or oil contamination on connectors.

Step 2: Sensor Circuit Testing Using a digital multimeter, disconnect the hydraulic oil temperature sensor connector and measure resistance across the sensor terminals. Compare readings against Komatsu specifications (typically 200-400 ohms at 20°C). Check for continuity in the wiring harness between the sensor and ECM connector pins.

Step 3: Cooling System Verification Test the hydraulic cooling fan operation by monitoring engagement during warm-up. Verify the fan motor voltage supply (typically 24V DC) and check the temperature-controlled relay function. Inspect the hydraulic oil cooler internally for blockages if external cleaning doesn't resolve overheating.

Step 4: Component Replacement If sensor resistance is out of specification or wiring shows damage, replace the temperature sensor (Komatsu part number specific to PC800-8R). For used machines, always apply dielectric grease to new connector pins to prevent corrosion. Clear codes using Komatsu diagnostic software (KOMTRAX) and monitor during operation.

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Disclaimer: This guide provides general diagnostic information. Always consult the official Komatsu service manual for your specific serial number and consider professional technician assistance for complex hydraulic system repairs.