Komatsu PC70-8 Fault Code H-6: Complete Diagnostic Guide

What is Komatsu PC70-8 Fault Code H-6?

Fault Code H-6 on the Komatsu PC70-8 indicates a hydraulic oil temperature sensor malfunction or abnormal temperature reading in the hydraulic system. This code is triggered when the Electronic Control Module (ECM) detects either an out-of-range signal from the temperature sensor or excessively high hydraulic oil temperatures that exceed safe operating parameters.

The hydraulic oil temperature sensor monitors fluid temperature to protect critical components from thermal damage. On the PC70-8, this sensor feeds real-time data to the ECM, which adjusts system performance and activates warnings when temperatures approach dangerous levels. Ignoring this code can lead to accelerated wear on hydraulic pumps, cylinders, and seals, potentially causing catastrophic system failure.

Common Symptoms

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

• Warning light illuminated on the instrument panel (often a hydraulic system indicator)
• Reduced hydraulic performance or derated power output as the ECM enters protective mode
• Sluggish boom, arm, or bucket movements due to system limitations
• Audible warning alarm in the cab during operation
• Intermittent code appearance that may correlate with heavy workload or high ambient temperatures

Potential Causes

The most common technical reasons for H-6 on used PC70-8 excavators include:

• Faulty hydraulic oil temperature sensor due to age-related degradation or internal failure
• Damaged or corroded wiring harness connections at the sensor plug (common wear point near the hydraulic tank)
• Actual hydraulic oil overheating caused by restricted oil cooler fins, low coolant flow, or failing cooling fan
• Contaminated hydraulic oil with incorrect viscosity affecting heat dissipation
• Intermittent short circuits or open circuits in sensor wiring from harness rubbing against frame components
• ECM calibration issues or software glitches (less common but possible in older machines)

How to Troubleshoot and Fix Code H-6

Step 1: Visual Inspection Begin by inspecting the hydraulic oil temperature sensor location (typically mounted on or near the hydraulic tank). Check for physical damage, oil leaks, and examine the connector for corrosion, bent pins, or moisture intrusion—common issues in used excavators.

Step 2: Electrical Testing Using a digital multimeter, disconnect the sensor and measure its resistance at ambient temperature (typically 2,000-3,000 ohms at 20°C, but verify against Komatsu specifications). Check wiring harness continuity from sensor to ECM and inspect for shorts to ground. Pay special attention to harness routing where cables contact metal surfaces.

Step 3: Verify Actual Temperature Use an infrared thermometer to measure actual hydraulic oil temperature and compare against sensor readings via Komatsu diagnostic software (KOMTRAX or compatible scan tool). If readings differ significantly, replace the sensor. If temperatures are genuinely high, inspect the hydraulic oil cooler, cooling fan operation, and oil condition.

Step 4: Component Replacement Replace the temperature sensor with a genuine Komatsu OEM part if testing confirms failure. For used machines, always apply dielectric grease to connectors during reassembly to prevent future corrosion. Clear codes and perform a test cycle under load.

---

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