What is Sumitomo SH350HD-6 Fault Code 118?

Fault Code 118 on the Sumitomo SH350HD-6 excavator 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 signals that the ECM has detected either an out-of-range voltage signal, an open circuit, or a short circuit within the coolant temperature sensor system.

The coolant temperature sensor plays a critical role in the SH350HD-6's engine management system by monitoring operating temperature and providing data to the ECM for fuel injection timing, idle speed control, and thermal protection protocols. When this sensor fails or sends erratic signals, the excavator's performance can be severely compromised, potentially leading to overheating, poor fuel economy, or engine protection shutdowns that halt jobsite productivity.

Common Symptoms

When Code 118 is active on your SH350HD-6, operators typically experience:

• Check engine warning light illuminated on the instrument cluster, sometimes accompanied by a coolant temperature warning
• Hard starting or rough idle, especially during cold starts when the ECM cannot properly adjust fuel delivery
• Engine derate mode activation, limiting power output to protect against potential overheating damage
• Cooling fan running continuously at high speed, regardless of actual engine temperature
• Erratic temperature gauge readings that fluctuate abnormally or display unrealistic values

Potential Causes

The most common technical causes for Code 118 on used SH350HD-6 excavators include:

• Faulty coolant temperature sensor due to internal element degradation (common after 5,000+ operating hours)
• Corroded or damaged wiring harness connectors at the sensor, particularly where the harness passes near the engine block or exhaust manifold
• Broken or chafed wiring along known rub points between the sensor and ECM, especially behind the engine mount area
• Poor ground connection at the sensor mounting point caused by corrosion or loose fasteners
• Contaminated coolant causing sensor fouling or coating that affects temperature reading accuracy
• ECM internal fault (less common) affecting the temperature sensor input circuit

How to Troubleshoot and Fix Code 118

Step 1: Visual Inspection Begin by locating the coolant temperature sensor (typically mounted on the engine block near the thermostat housing). Inspect the sensor connector for corrosion, moisture intrusion, bent pins, or physical damage. On used excavators, pay special attention to connector seals that may have degraded over time. Check the wiring harness from sensor to ECM for abrasion, particularly where it contacts frame members or vibrates against metal surfaces.

Step 2: Electrical Testing Disconnect the sensor connector and use a digital multimeter to measure resistance across the sensor terminals. At room temperature (68°F/20°C), resistance should typically read between 2,000-3,000 ohms (consult your service manual for exact specifications). Test the harness side for continuity to the ECM and check for shorts to ground. Measure supply voltage from the ECM (usually 5 volts reference) with the key on, engine off.

Step 3: Component Replacement and Verification If resistance values are out of specification or the sensor shows physical deterioration, replace the coolant temperature sensor with a genuine Sumitomo or OEM-equivalent part. Before installation, clean the mounting threads and apply appropriate thread sealant. After replacement, clear the fault code using diagnostic software (Sumitomo's proprietary system or compatible aftermarket tools) and perform a test run, monitoring live data to confirm proper temperature readings that correspond with actual engine warmth.

For used excavators specifically: Always inspect harness routing for previous repair attempts, zip-tie chafing, or modifications that may cause intermittent faults. Check coolant condition and replace if contaminated, as glycol breakdown can coat sensors and cause false readings.

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Disclaimer: This guide provides general diagnostic information for Sumitomo SH350HD-6 excavators. Always consult the manufacturer's service manual and consider professional diagnostic assistance for complex electrical issues. Improper repairs may lead to equipment damage or safety hazards.