Sumitomo SH350HD-5 Fault Code 107: Complete Diagnostic Guide

What is Sumitomo SH350HD-5 Fault Code 107?

Fault Code 107 on the Sumitomo SH350HD-5 excavator indicates an Engine Coolant Temperature (ECT) Sensor Circuit High Voltage condition. This code triggers when the Engine Control Module (ECM) detects an abnormally high voltage signal from the coolant temperature sensor circuit, typically exceeding 4.8-5.0 volts.

The ECT sensor is critical for the SH350HD-5's performance because it directly influences fuel injection timing, engine warm-up cycles, and cooling fan operation. When this sensor circuit malfunctions, the ECM cannot accurately monitor engine temperature, potentially leading to overheating, poor fuel economy, and reduced hydraulic system efficiency. On used machines, this code often appears after years of thermal cycling and vibration stress on electrical connections.

Common Symptoms

When Code 107 is active on your SH350HD-5, you may experience:

• Engine warning light illuminated on the instrument cluster, often accompanied by a continuous or intermittent alarm
• Hard starting conditions, especially during cold starts, as the ECM defaults to a fixed temperature value
• Cooling fan running continuously at high speed, even when the engine is cold
• Reduced engine power or derate mode activation to protect against perceived overheating
• Erratic temperature gauge readings or gauge stuck at maximum reading regardless of actual engine temperature

Potential Causes

The most common technical causes for Code 107 on used SH350HD-5 excavators include:

• Open circuit in the ECT sensor wiring harness, particularly at known rub points near the engine mount brackets and along the valve cover routing
• Failed ECT sensor with internal circuit degradation causing infinite resistance
• Corroded or damaged sensor connector pins, especially on machines operated in harsh or marine environments
• Wiring harness chafing against the engine block or hydraulic lines due to deteriorated mounting clips
• ECM internal circuit fault (rare, but possible on high-hour machines with 8,000+ operating hours)
• Poor ground connections at the engine block grounding points, creating voltage reference issues

How to Troubleshoot and Fix Code 107

Step 1: Visual Inspection Begin by inspecting the ECT sensor located on the engine block near the thermostat housing. Check the sensor connector for corrosion, bent pins, or moisture intrusion. On used excavators, pay special attention to the wiring harness routing—look for insulation wear, cracking, or evidence of rubbing against metal surfaces. Repair or replace damaged connectors before proceeding.

Step 2: Electrical Testing Using a digital multimeter (DMM), disconnect the ECT sensor connector and measure resistance across the sensor terminals. At 68°F (20°C), resistance should read approximately 2,000-3,000 ohms (consult your service manual for exact specifications). If the reading shows infinite resistance or open circuit, replace the sensor. Next, check the wiring harness for continuity from the sensor connector to the ECM—there should be less than 1 ohm resistance.

Step 3: Voltage Testing With the ignition ON and sensor disconnected, measure voltage at the harness connector. You should see approximately 5 volts on the signal wire. If voltage is absent or incorrect, trace the wiring for breaks or shorts. Check the ECM ground circuits at the engine block mounting points—clean and tighten all ground connections, as corroded grounds are common on older SH350HD-5 models.

Step 4: Advanced Diagnostics If sensor and wiring tests pass, connect Sumitomo diagnostic software (or compatible J1939 diagnostic tool) to read live ECT sensor data. Compare actual coolant temperature with sensor readings. For used excavators, verify the ECM software version is current, as outdated firmware can cause false high-voltage codes.

Disclaimer: This guide provides general diagnostic procedures for Code 107. Always consult the official Sumitomo SH350HD-5 service manual for model-specific specifications. If you're uncomfortable performing electrical diagnostics, contact a certified heavy equipment technician to prevent further damage to the electrical system or ECM.