What is Komatsu Fault Code E313?

Komatsu fault code E313 indicates a malfunction in the engine coolant temperature sensor circuit, specifically detecting an abnormal voltage signal or open/short circuit condition in the sensor wiring harness. This diagnostic trouble code (DTC) is generated when the Electronic Control Module (ECM) receives coolant temperature readings outside the normal operating parameters, typically below 0.1V or above 4.9V, suggesting the sensor or its circuit has failed.

This code is critical for Komatsu excavators because the coolant temperature sensor provides essential data that affects fuel injection timing, engine protection protocols, and emissions control. When the ECM cannot accurately monitor engine temperature, it may default to a fixed temperature value, potentially causing inefficient combustion, increased fuel consumption, and risk of engine overheating without proper warning. For used excavators, this sensor circuit is particularly vulnerable to age-related deterioration and environmental exposure.

Common Symptoms

• Check Engine Light or warning lamp illuminated on the instrument panel with possible temperature gauge malfunction
• Engine may experience hard starting or rough idle, especially during cold starts when accurate temperature readings are most critical
• Derate mode activation where engine power is automatically reduced to prevent potential damage from incorrect temperature assumptions
• Cooling fan running continuously at high speed regardless of actual engine temperature
• Increased black smoke from exhaust due to improper fuel-air mixture calibration based on faulty temperature data

Potential Causes

The most common technical causes for E313 on used Komatsu excavators include:

• Coolant temperature sensor failure due to internal resistance drift or element degradation after years of thermal cycling
• Wiring harness damage at known rub points near the engine block or cylinder head where vibration causes insulation wear
• Corroded or loose connector pins at the sensor plug, especially on machines operated in marine or high-moisture environments
• ECM internal circuit failure (less common) affecting the 5-volt reference voltage supply to the sensor
• Damaged sensor threads causing poor thermal contact with coolant passages, resulting in inaccurate readings

How to Troubleshoot and Fix Code E313

Step 1: Visual Inspection Begin by locating the coolant temperature sensor (typically mounted on the engine block or thermostat housing). Inspect the wiring harness from sensor to ECM for obvious damage, abrasion, or rodent damage. Check the sensor connector for corrosion, moisture intrusion, or pushed-back pins—common issues in used equipment.

Step 2: Electrical Testing Using a digital multimeter, disconnect the sensor and measure its resistance at various temperatures. At 68°F (20°C), resistance should typically read 2,000-3,000 ohms; consult your specific model's service manual for exact specifications. Test the harness continuity and check for shorts to ground using the ohmmeter function.

Step 3: Circuit Voltage Check With the sensor disconnected and ignition on (engine off), measure voltage at the harness connector. You should see approximately 5 volts reference voltage from the ECM. If voltage is absent or incorrect, trace the harness for breaks or check ECM pin connections.

Step 4: Sensor Replacement and Verification If sensor resistance is out of specification or harness testing reveals no issues, replace the coolant temperature sensor with a genuine Komatsu part. After installation, clear codes using Komatsu diagnostic software (KOMTRAX or compatible scan tool) and monitor for code recurrence during a complete heat cycle.

Critical for Used Excavators: Always apply dielectric grease to connectors during reassembly and secure harnesses away from heat sources and moving components to prevent future failures.

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Disclaimer: This guide provides general diagnostic information. Always consult your Komatsu service manual and consider professional diagnostic assistance for complex electrical issues or if you lack proper testing equipment.