Komatsu PC750-7 Fault Code H-6: Complete Diagnostic Guide

What is Komatsu PC750-7 Fault Code H-6?

Fault Code H-6 on the Komatsu PC750-7 indicates a hydraulic oil temperature sensor circuit malfunction or abnormally high hydraulic oil temperature. This code is triggered when the Electronic Control Module (ECM) detects either an electrical fault in the temperature sensor circuit or when hydraulic oil temperature exceeds the manufacturer's safe operating threshold (typically above 110-120°C or 230-248°F).

This fault is critical for the PC750-7 because excessive hydraulic oil temperature can cause rapid degradation of seals, reduced hydraulic efficiency, and potential component failure. The hydraulic system is the lifeblood of excavator operation, and temperature monitoring prevents catastrophic damage to pumps, motors, and control valves.

Common Symptoms

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

• Warning light or alarm illuminated on the monitor panel, often accompanied by an audible buzzer
• Reduced machine performance or automatic derate mode limiting hydraulic flow and engine RPM
• Sluggish hydraulic response in boom, arm, bucket, or swing functions
• Visible steam or heat emanating from the hydraulic tank area in severe cases
• Erratic temperature gauge readings or temperature display showing abnormally high or low values

Potential Causes

The most common technical causes for H-6 on used PC750-7 excavators include:

• Hydraulic oil temperature sensor failure due to age, contamination, or internal element degradation
• Damaged or corroded wiring harness at sensor connector or along routing path near hot engine components
• Insufficient hydraulic oil level causing inadequate cooling capacity
• Clogged hydraulic oil cooler restricting airflow or internal blockage reducing heat dissipation
• Faulty cooling fan operation or damaged fan drive motor/belt
• Contaminated hydraulic oil with incorrect viscosity reducing heat transfer efficiency
• Worn hydraulic pump generating excessive heat due to internal leakage

How to Troubleshoot and Fix Code H-6

Step 1: Visual Inspection Check hydraulic oil level using the sight glass with machine on level ground. Inspect the oil cooler for debris, bent fins, or blockage. Examine the cooling fan for proper operation and belt condition. On used excavators, carefully inspect the sensor wiring harness for chafing, especially where it routes near the hydraulic tank and frame—this is a known wear point on PC750 series machines.

Step 2: Sensor Circuit Testing Locate the hydraulic oil temperature sensor (typically mounted on the hydraulic tank). Disconnect the sensor connector and inspect for corrosion, oil contamination, or bent pins. Using a digital multimeter, measure sensor resistance at ambient temperature (should typically read 2,000-3,000 ohms at 20°C; consult service manual for exact specifications). Check for continuity in the wiring harness from sensor to ECM.

Step 3: Functional Testing If sensor resistance is out of specification, replace the temperature sensor with a genuine Komatsu part. Clear the fault code using Komatsu diagnostic software (KOMTRAX) or a compatible scan tool. If the sensor tests good, verify actual hydraulic oil temperature using an infrared thermometer—if temperature is genuinely high, address cooling system issues (clean cooler, replace fan motor, change contaminated oil). For persistent electrical faults on used machines, inspect the ECM connector for corrosion and check ground connections.

Disclaimer: This guide provides general diagnostic information. Always consult the official Komatsu PC750-7 service manual and consider professional assistance from certified Komatsu technicians for complex repairs or if you're unfamiliar with hydraulic systems and electrical diagnostics.