Komatsu PC750-7 Fault Code H-5: Complete Diagnostic Guide

What is Komatsu PC750-7 Fault Code H-5?

Fault Code H-5 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).

This fault is critical for the PC750-7 because excessive hydraulic oil temperature can cause rapid degradation of seals, reduced hydraulic efficiency, and potential damage to the hydraulic pump and control valves. The machine's monitoring system uses this sensor data to protect expensive hydraulic components from thermal damage.

Common Symptoms

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

• Hydraulic oil temperature warning light illuminated on the instrument panel
• Audible alarm sounding in the cab during operation
• Reduced hydraulic system performance or sluggish boom/arm movements
• Automatic engine derate or shutdown in severe cases to prevent component damage
• Visible steam or excessive heat radiating from the hydraulic tank area

Potential Causes

The most common technical causes for H-5 on used PC750-7 excavators include:

• Hydraulic oil temperature sensor failure due to age-related degradation or contamination
• Damaged or corroded wiring harness connections at the sensor (common rub point near hydraulic tank)
• Actual hydraulic system overheating from clogged hydraulic oil cooler fins or failed cooling fan
• Low hydraulic oil level causing inadequate heat dissipation
• ECM calibration issues or internal ECM faults (less common)
• Contaminated hydraulic oil reducing thermal transfer efficiency
• Failed hydraulic fan motor or damaged fan drive belt

How to Troubleshoot and Fix Code H-5

Step 1: Visual Inspection Check hydraulic oil level using the sight glass. Inspect the hydraulic oil cooler for debris, bent fins, or blockages. Verify the cooling fan operates when hydraulic temperature rises. On used excavators, carefully examine the sensor wiring harness routing near the hydraulic tank for chafing, cuts, or corroded connectors.

Step 2: Sensor Circuit Testing Using a digital multimeter, disconnect the temperature sensor connector and measure resistance across sensor terminals. Compare readings against Komatsu specifications (typically 200-400 ohms at 20°C). Check for voltage supply at the harness connector (should read approximately 5V reference voltage from ECM).

Step 3: Component Testing If circuit tests pass, monitor actual hydraulic oil temperature with an infrared thermometer during operation. Compare against sensor readings using Komatsu diagnostic software (KOMTRAX) or compatible scan tool. Replace the sensor if readings deviate by more than 10°C.

Step 4: System Verification Clean the hydraulic cooler thoroughly, replace contaminated oil if necessary, and clear the fault code. Operate the machine under load while monitoring temperatures. For persistent codes on used machines, inspect ECM ground connections and check for corrosion on all related circuit pins.

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Disclaimer: This guide provides general diagnostic information. Always consult the official Komatsu PC750-7 service manual and consider professional technician assistance for complex electrical diagnostics or hydraulic system repairs.