Komatsu PC450LC-8 Fault Code E-31: Complete Diagnostic Guide

What is Komatsu PC450LC-8 Fault Code E-31?

Fault Code E-31 indicates a malfunction in the engine coolant temperature sensor circuit or an abnormal coolant temperature reading detected by the Engine Control Module (ECM). This code specifically relates to the coolant temperature sensor sending irregular voltage signals outside the manufacturer's specified parameters (typically 0.5-4.5V range).

For the Komatsu PC450LC-8's SAA6D125E-5 engine, accurate coolant temperature monitoring is critical for proper fuel injection timing, engine protection systems, and hydraulic oil temperature management. When the ECM cannot reliably read coolant temperature, it may trigger protective derate modes that significantly impact machine performance and productivity.

Common Symptoms

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

• Engine warning light illuminated on the monitor panel with possible audible alarm
• Engine power derate or limited RPM output as the ECM enters protective mode
• Difficulty starting in cold conditions or excessive white smoke during warm-up
• Inaccurate coolant temperature readings on the display (showing extremely high or low values)
• Hydraulic system operating sluggishly due to ECM compensating for perceived temperature issues

Potential Causes

The most common technical reasons for E-31 on used PC450LC-8 excavators include:

• Coolant temperature sensor failure due to age-related degradation or internal short/open circuit
• Corroded or loose wiring harness connectors at the sensor or ECM (common at 5,000+ operating hours)
• Damaged sensor wiring from rubbing against engine components near the thermostat housing
• Contaminated coolant causing sensor element fouling or corrosion
• ECM internal circuit failure (less common but possible in high-hour machines)
• Intermittent ground connection issues in the sensor circuit

How to Troubleshoot and Fix Code E-31

Step 1: Visual Inspection Begin by inspecting the coolant temperature sensor located near the thermostat housing on the cylinder head. Check for physical damage, coolant leaks, or corrosion on the connector. On used excavators, examine the wiring harness for wear points where it contacts the engine block or routing brackets.

Step 2: Electrical Testing Using a digital multimeter, disconnect the sensor and measure resistance across its terminals. At 68°F (20°C), resistance should read approximately 2,000-3,000 ohms (consult service manual for exact specifications). Test harness continuity from sensor connector to ECM pins, checking for opens or shorts to ground.

Step 3: Live Circuit Analysis With the sensor connected and ignition on (engine off), backprobe the sensor connector and verify voltage supply from the ECM (should be approximately 5V reference). Monitor signal voltage while warming the engine—it should decrease smoothly from ~3.5V (cold) to ~0.5V (hot).

Step 4: Component Replacement If testing confirms sensor failure, replace with genuine Komatsu parts (part #6754-81-6120 or equivalent). For used machines, always apply dielectric grease to connectors and secure harnesses away from heat sources. Clear codes using Komatsu diagnostic software (KOMTRAX or compatible scan tool) and verify repair with a test cycle.

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Disclaimer: This guide provides general diagnostic information. Always consult the official Komatsu service manual for your specific machine serial number and consider professional technician assistance for complex electrical diagnostics or if you lack proper diagnostic equipment.