Komatsu PC110-7 Fault Code H-5: Complete Diagnostic Guide

What is Komatsu PC110-7 Fault Code H-5?

Fault Code H-5 on the Komatsu PC110-7 excavator indicates a hydraulic oil temperature sensor circuit malfunction or abnormal hydraulic oil overheat condition. This code is triggered when the Electronic Control Module (ECM) detects irregular voltage signals from the hydraulic oil temperature sensor or when the hydraulic system exceeds safe operating temperature thresholds (typically above 95°C/203°F).

This fault is critical for the PC110-7's performance because excessive hydraulic temperatures can cause rapid degradation of seals, hoses, and hydraulic fluid itself. The machine's control system relies on accurate temperature monitoring to protect expensive hydraulic components like the main pump, control valves, and hydraulic cylinders from thermal damage.

Common Symptoms

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

• Flashing or solid warning light on the instrument panel, often accompanied by an audible alarm
• Reduced hydraulic power or sluggish machine response as the ECM enters derate mode
• Noticeable heat around hydraulic tank or visible steam from cooling fins
• Irregular temperature gauge readings that spike or drop unexpectedly
• Machine shutdown in severe cases to prevent catastrophic hydraulic system damage

Potential Causes

For used PC110-7 excavators, this fault commonly stems from:

• Failed hydraulic oil temperature sensor due to prolonged exposure to heat cycles and vibration
• Damaged or corroded wiring harness at sensor connector points, especially where harnesses contact the frame near the hydraulic tank
• Genuinely overheated hydraulic oil caused by clogged cooling fins, failed cooling fan, or low oil levels
• Faulty ECM connections or ground circuit issues specific to the temperature monitoring circuit
• Contaminated hydraulic fluid with degraded viscosity properties causing excessive friction and heat generation

How to Troubleshoot and Fix Code H-5

Step 1: Visual Inspection Check the hydraulic oil level using the sight glass while machine is level. Inspect the hydraulic cooler fins for blockage from debris, dirt, or mud buildup. On used excavators, examine the wiring harness routing from the temperature sensor to the ECM, looking for chafing, cracking, or exposed copper wire—particularly where harnesses pass through bulkheads or contact metal edges.

Step 2: Sensor and Circuit Testing Locate the hydraulic temperature sensor (typically mounted on the hydraulic tank). Disconnect the sensor connector and inspect for corrosion, oil contamination, or bent pins—common issues in older machines. Using a digital multimeter, measure sensor resistance at ambient temperature (should read approximately 2-3 kΩ at 20°C). Check circuit continuity from sensor connector to the ECM pin (consult service manual for specific pin location). Verify ground circuit integrity with resistance under 5 Ω.

Step 3: Component Replacement and System Verification If sensor resistance is out of specification or wiring shows damage, replace the temperature sensor with genuine Komatsu parts (PN varies by serial number). For used excavators with high hours, replace the sensor connector pigtail simultaneously to prevent repeat failures from corroded terminals. After replacement, clear codes using Komatsu diagnostic software (KOMTRAX) or compatible scan tool, then operate machine through normal temperature cycles while monitoring live data.

Disclaimer: This guide provides general troubleshooting information. For used excavators with complex electrical issues or persistent codes, consult a certified Komatsu technician or authorized service center. Always disconnect battery power before performing electrical repairs.