Komatsu PC400-6 Fault Code H-5: Complete Diagnostic Guide

What is Komatsu PC400-6 Fault Code H-5?

Fault Code H-5 on the Komatsu PC400-6 indicates a hydraulic oil temperature sensor malfunction or abnormally high hydraulic oil temperature. This code is triggered when the Electronic Control Module (ECM) detects either a sensor circuit failure or when hydraulic oil temperature exceeds the safe operating threshold of approximately 110-120°C (230-248°F).

The hydraulic oil temperature sensor monitors the heat level in the hydraulic system, which is critical for maintaining proper viscosity and preventing component damage. On the PC400-6, this sensor feeds real-time data to the monitor panel, allowing the system to protect pumps, motors, and cylinders from thermal damage. Ignoring this code can lead to accelerated seal wear, reduced hydraulic efficiency, and catastrophic pump failure.

Common Symptoms

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

• Flashing warning light on the monitor panel with audible alarm
• Reduced hydraulic response or sluggish boom/arm/bucket movements
• Visible overheating of hydraulic oil tank with possible steam or hot oil smell
• Automatic derate mode limiting engine RPM to protect the hydraulic system
• Hydraulic oil appearing darker or burnt, indicating thermal breakdown

Potential Causes

The most common technical reasons for H-5 on used PC400-6 excavators include:

• Faulty hydraulic oil temperature sensor (common failure point after 8,000+ hours)
• Damaged or corroded wiring harness near the hydraulic tank where vibration causes wire chafing
• Plugged or restricted hydraulic oil cooler reducing heat dissipation capacity
• Low hydraulic oil level causing insufficient cooling circulation
• Failed cooling fan motor or damaged fan blades on the hydraulic cooler
• Excessive system pressure due to worn relief valves generating excess heat
• Contaminated hydraulic oil with incorrect viscosity grade

How to Troubleshoot and Fix Code H-5

Step 1: Visual Inspection Check hydraulic oil level using the sight glass. Inspect the oil cooler for debris, bent fins, or blockage. Examine the cooling fan for proper operation and blade condition.

Step 2: Sensor Circuit Testing Locate the hydraulic temperature sensor on the hydraulic tank (typically near the return filter). Using a multimeter, check sensor resistance at ambient temperature (should read approximately 2,000-3,000 ohms at 20°C). Inspect the connector pins for corrosion—a common issue on used machines exposed to moisture.

Step 3: Wiring Harness Verification Trace the sensor harness from the tank to the ECM, checking for rub points against the frame or hydraulic lines. On used excavators, pay special attention to areas where the harness passes near the swing motor or along the undercarriage where vibration damage occurs.

Step 4: Hydraulic System Assessment If sensor and wiring test normal, measure actual oil temperature using an infrared thermometer. If temperature exceeds 110°C during normal operation, investigate cooler efficiency, fan operation, and system pressure settings using Komatsu diagnostic software (KOMTRAX).

Disclaimer: This guide provides general troubleshooting information. Always consult the official Komatsu service manual and consider professional diagnostic assistance for complex hydraulic system issues.