Komatsu PC800SE-8R Fault Code E-31: Complete Diagnostic Guide

What is Komatsu PC800SE-8R 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 mounted in the engine block. When the sensor signal falls outside predetermined voltage parameters or indicates excessive temperature, the system triggers E-31. For the PC800SE-8R, this is particularly critical because improper coolant temperature management can lead to reduced hydraulic efficiency, increased component wear, and potential catastrophic engine failure in high-demand excavation operations.

Common Symptoms

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

• Engine warning light illuminated on the monitor panel with audible alarm
• Reduced engine power or automatic derate mode to protect the engine from thermal damage
• Inaccurate or erratic coolant temperature gauge readings (showing extremely high or low temperatures)
• Engine may fail to start if ECM detects unsafe temperature conditions
• Increased cooling fan operation running continuously at high speed

Potential Causes

The most common technical causes for E-31 in used PC800SE-8R excavators include:

• Faulty coolant temperature sensor due to internal thermistor degradation (common after 8,000+ operating hours)
• Damaged or corroded wiring harness connections at the sensor plug, especially where harness routes near hot exhaust components
• Broken or chafed wires in the sensor circuit caused by engine vibration and harness movement
• ECM internal fault or corrupted calibration data (less common but possible in high-hour machines)
• Actual engine overheating due to cooling system failures (low coolant, failed thermostat, clogged radiator)
• Poor ground connections at engine block grounding points causing voltage reference issues

How to Troubleshoot and Fix Code E-31

Step 1: Visual Inspection Begin by inspecting the coolant temperature sensor located on the engine block's coolant passage. Check for physical damage, coolant leaks, and corrosion on the connector pins. For used excavators, carefully examine the entire wiring harness from sensor to ECM for rub points, especially where it passes near the turbocharger and exhaust manifold.

Step 2: Electrical Testing Using a digital multimeter, disconnect the sensor and measure its resistance at ambient temperature (typically 2,000-3,000 ohms at 20°C for Komatsu sensors). Compare readings against manufacturer specifications. Check circuit continuity from sensor connector to ECM pins and verify ground integrity (should read less than 1 ohm resistance).

Step 3: Signal Voltage Verification With ignition on and sensor connected, backprobe the sensor connector to measure supply voltage (should be approximately 5 volts from ECM). Monitor signal voltage while engine warms up—it should decrease smoothly from ~4 volts (cold) to ~1 volt (operating temperature).

Step 4: Advanced Diagnostics Connect Komatsu KOMTRAX or compatible diagnostic software to read live sensor data and freeze frame information. This reveals whether the fault is intermittent or constant. For used machines, perform a harness wiggle test while monitoring live data to identify intermittent connection issues.

Step 5: Component Replacement If testing confirms sensor failure, replace with genuine Komatsu parts (part number specific to SAA6D140E-7 engine). After replacement, clear codes and perform a complete heat cycle test to verify proper operation.

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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 diagnosis for complex electrical issues or if you lack proper diagnostic equipment.