Komatsu PC50MR-2 Fault Code H-6: Complete Diagnostic Guide

What is Komatsu PC50MR-2 Fault Code H-6?

Fault Code H-6 on the Komatsu PC50MR-2 indicates a hydraulic oil temperature sensor malfunction or abnormally high hydraulic oil temperature in the hydraulic system. This code is triggered when the hydraulic temperature sensor detects temperatures exceeding the safe operating threshold (typically above 95°C/203°F) or when the sensor circuit experiences voltage irregularities.

The hydraulic system in the PC50MR-2 mini excavator relies on precise temperature monitoring to prevent component damage and maintain optimal viscosity. When hydraulic oil overheats, it loses lubrication properties, accelerates seal degradation, and can cause catastrophic pump failure. The electronic control module (ECM) continuously monitors this sensor to protect the machine's expensive hydraulic components.

Common Symptoms

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

• Hydraulic temperature warning light illuminated on the instrument panel (usually red or amber)
• Reduced hydraulic performance including slower cycle times and weak digging force
• Automatic engine derate to idle speed when critical temperature thresholds are exceeded
• Audible warning alarm that sounds continuously until the issue is addressed
• Hot hydraulic oil smell or visible vapor from the hydraulic tank breather cap

Potential Causes

The most common technical causes for H-6 on used PC50MR-2 excavators include:

• Hydraulic temperature sensor failure due to internal element degradation (common after 5,000+ hours)
• Damaged sensor wiring harness from rubbing against the swing motor frame near the turntable
• Corroded sensor connector pins from moisture intrusion at the hydraulic tank mounting location
• Actual hydraulic oil overheating caused by plugged hydraulic oil cooler fins or failed cooling fan
• Low hydraulic oil level resulting in insufficient thermal mass and rapid temperature rise
• Malfunctioning hydraulic pump generating excessive heat from internal wear
• Contaminated hydraulic oil with improper viscosity ratings for operating conditions

How to Troubleshoot and Fix Code H-6

Step 1: Initial Visual Inspection Before diagnosing electrical issues, check the hydraulic oil level using the sight glass on the tank. Inspect the hydraulic oil cooler for debris buildup blocking airflow. On used machines, check for oil leaks around the pump case and cylinder rod seals that could indicate low fluid levels.

Step 2: Sensor Circuit Testing Using a digital multimeter, disconnect the temperature sensor connector (located on the hydraulic tank, driver's side) and measure resistance. At 25°C (77°F), resistance should read approximately 2.4-2.6 kΩ. Compare readings against Komatsu's temperature-resistance chart. Check for voltage supply at the harness connector—should read approximately 5 volts DC with the ignition on.

Step 3: Harness and Connector Inspection Inspect the sensor wiring harness from the tank to the main ECM connector under the operator's seat. On used PC50MR-2 models, check for wire chafing where the harness passes through the bulkhead near the swing bearing. Clean all connector pins with electrical contact cleaner and check for green corrosion—a common issue in machines stored outdoors.

Step 4: Functional Testing If sensor resistance and voltage are correct, use Komatsu diagnostic software (KOMTRAX) or a compatible scan tool to monitor live temperature data. Compare sensor readings with an infrared thermometer measurement of actual hydraulic oil temperature. A variance greater than 10°C indicates sensor replacement is needed.

Step 5: Component Replacement Replace the hydraulic temperature sensor (Komatsu Part #7861-93-3320 or equivalent). After installation, clear fault codes and operate the machine under load for 20 minutes, monitoring temperature readings. For used excavators, always replace the O-ring seal during sensor installation to prevent oil seepage.

---

Professional Disclaimer: While this guide provides comprehensive troubleshooting procedures, hydraulic system diagnostics on heavy equipment require proper training and safety protocols. Always consult the official Komatsu PC50MR-2 service manual and consider professional assistance for complex repairs. Improper diagnosis can lead to equipment damage or personal injury.