Komatsu PC800SE-7 Fault Code E-31: Complete Diagnostic Guide

What is Komatsu PC800SE-7 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 monitoring system, which is critical for preventing engine overheating and maintaining optimal operating temperatures in the Komatsu SAA6D140E-7 engine.

The ECM continuously monitors coolant temperature through a thermistor-type sensor that changes resistance based on temperature. When the sensor signal falls outside predetermined parameters—either showing implausibly high/low temperatures or circuit irregularities—the system triggers E-31. For the PC800SE-7, this is particularly critical because improper coolant temperature readings can lead to incorrect fuel injection timing, reduced engine performance, and potential catastrophic engine damage in heavy-duty excavation operations.

Common Symptoms

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

• Warning light illumination on the monitor panel with possible audible alarm
• Engine derate mode activation, limiting maximum RPM and hydraulic performance
• Erratic temperature gauge readings or gauge stuck at minimum/maximum positions
• Difficulty starting in cold conditions or excessive cooling fan operation
• Black smoke from exhaust due to improper fuel mixture compensation

Potential Causes

The most common technical causes for E-31 on used PC800SE-7 excavators include:

• Coolant temperature sensor failure due to age-related degradation or thermal cycling damage
• Wiring harness damage at known rub points near the engine block or turbocharger heat shield
• Corroded or loose connector pins at the sensor or ECM connection points (common in machines with 5,000+ hours)
• ECM internal circuit failure affecting the temperature monitoring channel
• Coolant contamination causing sensor element coating or failure
• Ground circuit issues specific to the engine harness ground points

How to Troubleshoot and Fix Code E-31

Step 1: Visual Inspection Begin by inspecting the coolant temperature sensor located on the engine block near the thermostat housing. Check for physical damage, coolant leaks, or corrosion on the connector terminals. On used excavators, carefully examine the wiring harness for chafing against the engine block, heat damage from exhaust components, or previous repair attempts.

Step 2: Electrical Testing Using a digital multimeter, disconnect the sensor and measure resistance across the sensor terminals. At 20°C (68°F), resistance should typically read 2,000-3,000 ohms (consult your service manual for exact specifications). Test the harness continuity from sensor connector to ECM pins, checking for opens or shorts to ground. Verify supply voltage (typically 5V reference) at the sensor connector with ignition on.

Step 3: Advanced Diagnostics Connect Komatsu KOMTRAX diagnostic software or compatible scan tool to read live sensor data and freeze frame information. Compare actual coolant temperature (using infrared thermometer) against displayed values. Check for intermittent connections by wiggling harnesses while monitoring data. Inspect ECM connector pins for corrosion—a common issue in high-hour machines.

Step 4: Repair and Verification Replace faulty components starting with the most likely cause. For used equipment, always replace connector seals and apply dielectric grease to prevent future corrosion. After repairs, clear codes, perform a cold start cycle, and monitor temperature readings through full operating range.

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Disclaimer: This guide provides general diagnostic information. Always consult the official Komatsu service manual for your specific machine serial number. Complex electrical diagnostics should be performed by qualified technicians with proper diagnostic equipment. Improper repairs may void warranties or cause additional damage.