Sumitomo SH350HD-5 Fault Code 2104: Complete Diagnostic Guide

What is Sumitomo SH350HD-5 Fault Code 2104?

Fault Code 2104 on the Sumitomo SH350HD-5 excavator indicates an Engine Coolant Temperature (ECT) Sensor Circuit High Voltage condition. This diagnostic trouble code (DTC) 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 a critical thermistor-type component that monitors engine coolant temperature and sends variable resistance signals to the ECM. On the SH350HD-5's Isuzu engine platform, this sensor directly influences fuel injection timing, cooling fan operation, and engine protection protocols. When Code 2104 appears, the ECM assumes a default coolant temperature value, which can compromise engine efficiency and trigger protective measures that reduce machine productivity.

Common Symptoms

When Code 2104 is active on your SH350HD-5, operators typically experience:

• Engine warning light illuminated on the instrument cluster with possible audible alarm
• Cooling fan running continuously at high speed, even during cold starts
• Reduced engine power or derate mode activation to prevent potential overheating damage
• Hard starting conditions or rough idle, especially in cold ambient temperatures
• Inaccurate temperature gauge readings, often displaying maximum temperature or erratic fluctuations

Potential Causes

For used SH350HD-5 excavators, this fault code commonly stems from:

• Open circuit or damaged wiring harness between the ECT sensor and ECM, particularly at flex points near the engine mount where vibration causes wire fatigue
• Corroded or loose connector terminals at the sensor plug, especially on machines operating in wet or corrosive environments
• Failed ECT sensor with internal open circuit (less common than wiring issues)
• Chafed wiring insulation rubbing against engine components, creating intermittent short-to-ground conditions that resolve when the harness moves
• ECM-side connector corrosion or damaged pins at the controller harness interface
• Previous repair attempts using incorrect sensor specifications or improper connector repairs

How to Troubleshoot and Fix Code 2104

Step 1: Visual Inspection of Wiring and Connectors Begin by thoroughly inspecting the ECT sensor wiring harness from the sensor (typically located near the thermostat housing) to the ECM. On used excavators, pay special attention to areas where the harness routes near sharp edges, exhaust components, or vibration points. Look for abraded insulation, melted wire covering, or obvious breaks. Disconnect the sensor connector and inspect for corrosion, moisture intrusion, or bent pins—clean with electrical contact cleaner if needed.

Step 2: Test the ECT Sensor Disconnect the sensor and use a digital multimeter (DMM) to measure resistance across the sensor terminals. At room temperature (68°F/20°C), resistance should typically read 2,000-3,000 ohms (consult service manual for exact specifications). Compare readings at different temperatures using an infrared thermometer. A reading of infinite resistance (open circuit) confirms sensor failure. For used machines, even marginal sensors showing resistance values 20% outside specifications should be replaced.

Step 3: Circuit Voltage Testing With the sensor disconnected and ignition on (engine off), measure voltage at the harness connector leading to the sensor. You should see approximately 5 volts on the signal wire—this is the reference voltage from the ECM. A constant 12V or battery voltage indicates a wiring short to a power source. Measure continuity to ground on the signal wire; any continuity suggests a short-circuit condition requiring harness repair or replacement.

Step 4: Verify ECM Ground and Signal Integrity Check the ECM ground connections for tightness and corrosion, as poor grounds can cause erratic sensor readings. Use your diagnostic software (Sumitomo-specific or compatible J1939 scanner) to monitor live ECT sensor voltage while gently wiggling the harness—voltage spikes indicate intermittent wiring faults common in high-hour used equipment.

Disclaimer: This guide provides general diagnostic information for experienced technicians. Always consult the official Sumitomo service manual for your specific serial number range. If unfamiliar with electrical diagnostics or high-voltage systems, seek qualified professional assistance to prevent equipment damage or personal injury.