Sumitomo SH240-5 Fault Code 118: Complete Diagnostic Guide

What is Sumitomo SH240-5 Fault Code 118?

Fault Code 118 on the Sumitomo SH240-5 excavator indicates a malfunction in the engine coolant temperature sensor circuit or an abnormal coolant temperature reading detected by the ECM (Engine Control Module). This diagnostic trouble code (DTC) specifically monitors the thermistor-type sensor that measures engine coolant temperature and transmits voltage signals to the controller.

This code is critical because the ECM relies on accurate coolant temperature data to manage fuel injection timing, engine warm-up cycles, and protective shutdown sequences. When Code 118 triggers, the engine management system may default to limp mode or implement power derate to prevent potential overheating damage to the engine block and cylinder head.

Common Symptoms

When Code 118 is active on your SH240-5, operators typically experience:

• Engine warning lamp illuminated on the instrument cluster (amber or red depending on severity)
• Reduced engine power or RPM limitations during operation
• Difficulty starting the engine, especially during cold conditions
• Erratic temperature gauge readings or gauge stuck at minimum/maximum positions
• Engine fan running continuously at high speed regardless of actual temperature
• Potential activation of automatic engine shutdown if critical temperature thresholds are exceeded

Potential Causes

The most common technical causes for Code 118 in used SH240-5 excavators include:

• Coolant temperature sensor failure due to age-related degradation or internal resistance drift
• Damaged wiring harness between the sensor and ECM, particularly at flex points near the engine block
• Corroded or loose connector pins at the sensor plug or ECM interface
• Shorted or open circuit in the sensor signal wire (typically a 5-volt reference circuit)
• Low coolant level causing sensor exposure to air instead of coolant
• ECM internal circuit failure (less common but possible in high-hour machines)
• Aftermarket sensor installation with incorrect resistance specifications

How to Troubleshoot and Fix Code 118

Step 1: Visual Inspection Begin by checking the coolant level in the radiator and expansion tank. Inspect the coolant temperature sensor (typically located on the thermostat housing or cylinder head) for physical damage, coolant leaks, or corrosion. On used excavators, carefully examine the wiring harness from the sensor to the ECM for chafing, particularly where it passes near moving components or sharp edges.

Step 2: Electrical Testing Using a digital multimeter, disconnect the sensor connector and 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). Check for continuity in the wiring between the sensor connector and ECM pins. Measure voltage at the sensor connector with ignition on—you should see approximately 5 volts on the reference wire.

Step 3: Component Replacement and Verification If resistance values are out of specification or wiring shows damage, replace the faulty component. For used machines, always clean connector terminals with electrical contact cleaner and apply dielectric grease before reconnection. After repairs, clear the fault code using Sumitomo diagnostic software or a compatible scan tool, then operate the machine through a full warm-up cycle to verify the repair.

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Disclaimer: This guide provides general troubleshooting information. Always consult the official Sumitomo service manual for your specific machine serial number. If you're unfamiliar with electrical diagnostics or heavy equipment systems, contact a certified Sumitomo technician to prevent further damage or safety hazards.