Komatsu PC650LC-8R Fault Code E-31: Complete Diagnostic Guide

What is Komatsu PC650LC-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 sensor sending irregular voltage signals to the ECM, preventing accurate monitoring of engine operating temperature.

For the Komatsu PC650LC-8R's SAA6D140E-6 engine, maintaining proper coolant temperature monitoring is critical. The ECM relies on this data to adjust fuel injection timing, control engine speed, and prevent overheating damage. When E-31 triggers, the engine management system cannot properly regulate performance, potentially leading to reduced efficiency or engine protection mode activation.

Common Symptoms

When fault code E-31 is active, operators typically experience:

• Engine warning light illuminated on the monitor panel with E-31 displayed
• Engine derate or power reduction as the ECM enters protective mode
• Difficulty starting when the engine is cold, or rough idle conditions
• Cooling fan running continuously at high speed regardless of actual temperature
• Inaccurate temperature gauge readings showing extreme high or low values inconsistently

Potential Causes

The most common technical causes for E-31 on used PC650LC-8R excavators include:

• Coolant temperature sensor failure due to age-related degradation or internal short/open circuit
• Damaged wiring harness between the sensor and ECM, particularly at known rub points near the engine mounting brackets
• Corroded or loose connector pins at the sensor plug or ECM connection points
• ECM internal fault affecting the temperature sensor input circuit (less common)
• Contaminated coolant causing sensor element fouling or corrosion
• Poor ground connection at the sensor mounting location affecting signal integrity

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 around the sensor, and examine the wiring harness for abrasion, cuts, or heat damage. On used excavators, pay special attention to harness routing near moving components.

Step 2: Connector and Resistance Testing Disconnect the sensor connector and inspect for corrosion, bent pins, or moisture. Using a digital multimeter, measure the sensor's resistance. At room temperature (20°C/68°F), resistance should typically read 2,000-3,000 ohms. Compare readings against Komatsu specifications in the service manual. Test resistance at different temperatures if possible.

Step 3: Circuit Voltage Testing With the sensor disconnected and ignition on, measure voltage at the ECM-side connector. You should see approximately 5 volts reference voltage from the ECM. If voltage is absent or incorrect, inspect wiring continuity between the sensor and ECM connector pins, checking for shorts to ground or open circuits.

Step 4: Sensor Replacement and Verification If the sensor tests outside specifications or wiring shows damage, replace the faulty component using genuine Komatsu parts (part number 6261-81-6510 or equivalent). After replacement, clear the fault code using Komatsu diagnostic software (KOMTRAX) or a compatible scan tool, then monitor for code recurrence during operation.

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 ECM-related issues.