Komatsu WA600-3 Fault Code H-31: Complete Diagnostic Guide

What is Komatsu WA600-3 Fault Code H-31?

Fault Code H-31 indicates a hydraulic oil temperature sensor circuit malfunction in the Komatsu WA600-3 wheel loader. This code triggers when the machine's Electronic Control Module (ECM) detects an abnormal signal from the hydraulic oil temperature sensor, which monitors the operating temperature of the hydraulic system fluid.

The hydraulic oil temperature sensor plays a critical role in protecting the WA600-3's hydraulic system from overheating damage. When this sensor fails or sends erratic signals, the ECM cannot accurately monitor hydraulic fluid temperatures, potentially leading to component damage, reduced hydraulic efficiency, and premature system wear. For used machines with thousands of operating hours, this sensor circuit is particularly vulnerable to degradation.

Common Symptoms

When Code H-31 is active, operators typically experience:

• Warning light illuminated on the instrument cluster, specifically the hydraulic system indicator
• Intermittent or constant alarm sounding in the cab during operation
• Reduced hydraulic performance or sluggish loader/bucket response in some cases
• ECM derate mode activation, limiting engine RPM to protect the hydraulic system
• Inaccurate temperature gauge readings on the dashboard display

Potential Causes

The most common technical reasons for H-31 on used WA600-3 machines include:

• Failed hydraulic oil temperature sensor due to internal element degradation or contamination exposure
• Damaged or corroded wiring harness connections at the sensor plug (common wear point near hydraulic tank)
• Chafed sensor wiring from rubbing against frame components or hydraulic lines during machine operation
• Corroded connector pins at the sensor or ECM interface due to moisture intrusion
• Open or short circuit in the sensor signal wire between the sensor and ECM
• ECM internal fault (rare, but possible in high-hour used machines)

How to Troubleshoot and Fix Code H-31

Step 1: Visual Inspection Begin by locating the hydraulic oil temperature sensor (typically mounted on the hydraulic tank). Inspect the sensor body for physical damage, oil contamination, or loose mounting. Examine the wiring harness from sensor to ECM for visible chafing, cuts, or heat damage—pay special attention to areas where wires contact metal edges.

Step 2: Electrical Testing Disconnect the sensor connector and use a digital multimeter to check sensor resistance. At room temperature (20°C/68°F), resistance should typically read between 2,000-3,000 ohms (consult your service manual for exact specifications). Check for continuity in the wiring harness from sensor connector to ECM. Measure voltage supply at the sensor connector with ignition on—should read approximately 5 volts.

Step 3: Connector and Ground Verification Clean all connector pins with electrical contact cleaner and inspect for corrosion or bent terminals. For used excavators, corrosion is a primary failure point. Verify proper ground connection at both the sensor and ECM. Check harness routing for potential rub points that may have developed over the machine's service life.

Step 4: Component Replacement If sensor resistance is out of specification or wiring shows damage, replace the faulty component. When installing a new temperature sensor, apply anti-seize compound to threads and ensure proper torque specifications. After repairs, clear codes using Komatsu diagnostic software (KOMTRAX or equivalent) and perform a test cycle.

Disclaimer: This guide provides general diagnostic information. 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 or qualified heavy equipment mechanic.