Komatsu PC400-6 Fault Code E231: Complete Diagnostic Guide

What is Komatsu PC400-6 Fault Code E231?

Fault Code E231 on the Komatsu PC400-6 indicates a malfunction in the engine coolant temperature sensor circuit, specifically detecting an abnormally high voltage signal or open circuit condition.

This diagnostic trouble code is generated by the Engine Control Module (ECM) when the coolant temperature sensor signal falls outside the manufacturer's specified parameters (typically above 4.9V). The sensor, a negative temperature coefficient (NTC) thermistor, provides critical data for fuel injection timing, cold-start enrichment, and cooling fan activation.

On the PC400-6's SA6D125E-2 engine, accurate coolant temperature readings are essential for optimal combustion efficiency and preventing thermal damage. An unresolved E231 code can lead to improper fuel metering and potential engine overheating.

Common Symptoms

• Warning lamp illumination on the monitor panel with E231 displayed
• Engine running in derate mode with reduced power output
• Erratic idle behavior or rough running, especially during cold starts
• Cooling fan running continuously or not engaging at all
• Inaccurate temperature gauge readings or gauge showing maximum/minimum values

Potential Causes

• Faulty coolant temperature sensor – internal failure common in high-hour machines
• Open or corroded wiring in the sensor harness, particularly near exhaust manifold routing
• Damaged connector pins at the sensor or ECM connection points
• Chafed wiring harness where it contacts the engine block or frame brackets
• ECM ground circuit issues causing reference voltage problems
• Previous improper repairs using non-OEM splices or connectors

How to Troubleshoot and Fix Code E231

Step 1: Visual Inspection Locate the coolant temperature sensor on the engine block near the thermostat housing. Inspect the wiring harness for abrasion, heat damage, or rodent damage. On used PC400-6 units, pay particular attention to harness routing near hot exhaust components and frame contact points where vibration causes wear.

Step 2: Electrical Testing Using a digital multimeter, disconnect the sensor connector and measure resistance across the sensor terminals. At 20°C (68°F), expect approximately 2.5kΩ; at 80°C (176°F), approximately 300Ω. An open circuit reading (OL) confirms sensor failure. Also verify 5V reference voltage at the harness connector with the key on.

Step 3: Connector and Harness Verification Clean all connector pins with electrical contact cleaner and inspect for corrosion or green oxidation. Check continuity from the sensor connector to the ECM using Komatsu's wiring diagrams. Repair any damaged wiring with proper heat-shrink splices and weatherproof connectors.

Step 4: Component Replacement If testing confirms sensor failure, install a genuine Komatsu replacement sensor and clear the fault code using Komatsu VHMS diagnostic software or equivalent scan tool.

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Disclaimer: This guide is for informational purposes only. Always consult qualified heavy equipment technicians and refer to official Komatsu service manuals for your specific machine serial number before performing repairs.