Komatsu PC450-8 Fault Code H-6: Complete Diagnostic Guide

What is Komatsu PC450-8 Fault Code H-6?

Fault Code H-6 indicates a hydraulic oil temperature sensor circuit malfunction in the Komatsu PC450-8 excavator. This code is triggered when the Electronic Control Module (ECM) detects an abnormal voltage signal from the hydraulic oil temperature sensor, typically indicating an open circuit, short circuit, or sensor reading outside the normal operating range (usually -40°C to 150°C).

This fault is critical because the hydraulic system's temperature directly affects oil viscosity, component protection, and overall machine performance. The ECM relies on accurate temperature data to prevent overheating damage to pumps, motors, and cylinders. When this sensor fails, the machine may enter a protective derate mode or display inaccurate temperature readings, potentially leading to catastrophic hydraulic system failure if ignored.

Common Symptoms

• Hydraulic oil temperature warning light illuminated on the monitor panel
• Machine derate or reduced hydraulic power output as a protective measure
• Inaccurate or frozen temperature readings on the operator display (often showing -40°C or maximum values)
• Intermittent code activation during cold starts or after extended operation
• Possible activation of additional warning alarms or buzzer alerts

Potential Causes

The most common causes for Code H-6 in used PC450-8 excavators include:

• Damaged or corroded sensor connector at the hydraulic tank (common failure point due to heat exposure and vibration)
• Failed hydraulic oil temperature sensor (NTC thermistor type) due to age or contamination
• Wiring harness damage between the sensor and ECM, particularly at rub points near the hydraulic tank mounting area
• Corroded or loose ground connections affecting sensor circuit integrity
• ECM internal fault (rare, but possible in high-hour machines)
• Contaminated hydraulic oil causing sensor element degradation

How to Troubleshoot and Fix Code H-6

Step 1: Visual Inspection Begin by inspecting the hydraulic oil temperature sensor located on the hydraulic tank. Check the connector for corrosion, oil contamination, or bent pins. On used excavators, this connector frequently suffers from heat cycling damage. Clean contacts with electrical contact cleaner and inspect the wiring harness for chafing or breaks, especially where it routes near moving components.

Step 2: Sensor Resistance Testing Disconnect the sensor and use a digital multimeter to measure resistance across the sensor terminals. At 20°C (68°F), resistance should typically read between 2,000-3,000 ohms (consult your service manual for exact specifications). Compare readings at different temperatures using a heat gun or cold spray. If readings are infinite (open circuit) or zero (short circuit), replace the sensor.

Step 3: Circuit Voltage Check With the sensor disconnected and ignition on, measure voltage at the harness connector. You should see approximately 5 volts on the signal wire (reference voltage from ECM). If voltage is absent, trace the harness back to the ECM for breaks or shorts. Check ground continuity to ensure less than 1 ohm resistance.

Step 4: Advanced Diagnostics Use Komatsu KOMTRAX or compatible diagnostic software to monitor live sensor data. Compare actual hydraulic oil temperature (measured with an infrared thermometer) against displayed values. For used machines, inspect the hydraulic oil condition—contaminated oil can coat the sensor element, causing false readings.

Disclaimer: This guide provides general troubleshooting procedures. Always consult the official Komatsu service manual for your specific machine serial number. If you're uncomfortable performing electrical diagnostics, contact a certified Komatsu technician to prevent further damage or safety hazards.