Sumitomo SH240-5 Fault Code 107: Complete Diagnostic Guide

What is Sumitomo SH240-5 Fault Code 107?

Fault Code 107 on the Sumitomo SH240-5 excavator indicates an Engine Coolant Temperature (ECT) Sensor Circuit High Voltage condition. This diagnostic trouble code is triggered when the Engine Control Module (ECM) detects an abnormally high voltage signal from the coolant temperature sensor circuit, typically above 4.8-4.9 volts.

The ECT sensor is critical for proper engine management on this Komatsu-powered excavator. It provides real-time coolant temperature data that the ECM uses to adjust fuel injection timing, idle speed, and cooling fan operation. When Code 107 activates, the ECM enters a failsafe mode using default temperature values, which can significantly impact engine performance and fuel efficiency.

Common Symptoms

When Code 107 is active on your SH240-5, you may experience:

• Check Engine light illuminated on the instrument panel
• Hard starting or difficult cold starts, as the ECM cannot properly adjust fuel enrichment
• Cooling fan running continuously at high speed, even when engine is cold
• Poor fuel economy and rough idle due to incorrect fuel mapping
• Engine derate mode where maximum RPM is limited to protect the engine from potential overheating

Potential Causes

The most common technical reasons for Code 107 on used SH240-5 excavators include:

• Open circuit in the ECT sensor wiring harness, often caused by wire breakage near the engine block mounting points where vibration is highest
• Failed ECT sensor with internal open circuit (common after 5,000+ operating hours)
• Corroded or damaged connector at the sensor or ECM harness connection point
• Damaged sensor wiring due to heat exposure from exhaust manifold proximity or rubbing against engine components
• ECM internal fault (rare, but possible in high-hour machines with moisture intrusion)

How to Troubleshoot and Fix Code 107

Step 1: Visual Inspection Begin by inspecting the ECT sensor location on the engine block (typically on the thermostat housing). Check for physical damage, coolant leaks, or corrosion on the two-pin connector. On used excavators, pay special attention to wire chafing points where the harness routes along the valve cover.

Step 2: Electrical Testing Disconnect the ECT sensor connector. Using a digital multimeter, measure resistance across the sensor terminals. At room temperature (68°F/20°C), resistance should read approximately 2,000-3,000 ohms. A reading of infinite resistance (OL) confirms sensor failure. Also check for continuity between each sensor pin and ground—there should be none.

Step 3: Wiring Harness Verification With the sensor disconnected, measure voltage at the harness connector (ECM side) with ignition on. You should see approximately 5 volts on the signal wire. If voltage is absent, trace the harness back to the ECM for breaks or shorts. Check connector terminals for corrosion—a common issue in older machines exposed to moisture.

Step 4: Repair or Replace If the sensor tests faulty, replace it with an OEM-equivalent ECT sensor (Komatsu part number recommended for reliability). If wiring is damaged, repair using high-temperature automotive wire and heat-shrink connectors rated for 200°C+. After repairs, clear codes using diagnostic software and perform a test cycle.

Disclaimer: This guide provides general diagnostic information. Always consult the Sumitomo SH240-5 service manual and consider professional assistance for complex electrical diagnostics. Improper repairs can lead to engine damage or safety hazards.