Sumitomo SH220LC-6 Fault Code 118: Complete Diagnostic Guide

What is Sumitomo SH220LC-6 Fault Code 118?

Fault Code 118 on the Sumitomo SH220LC-6 indicates a malfunction in the engine coolant temperature sensor circuit, specifically detecting an abnormal voltage signal or open circuit condition in the coolant temperature monitoring system.

This diagnostic trouble code (DTC) is generated when the Engine Control Module (ECM) detects voltage readings outside the acceptable range from the coolant temperature sensor (typically below 0.2V or above 4.8V). The ECM relies on accurate coolant temperature data to optimize fuel injection timing, engine warm-up cycles, and hydraulic system performance. On used excavators like the SH220LC-6, this sensor plays a critical role in preventing engine overheating and ensuring proper diesel combustion efficiency, making early diagnosis essential to avoid catastrophic engine damage.

Common Symptoms

When Fault Code 118 is active on your Sumitomo SH220LC-6, operators typically experience:

• Engine warning light illuminated on the instrument cluster, often accompanied by a check engine indicator
• Hard starting conditions, especially during cold weather, as the ECM cannot properly adjust fuel delivery
• Erratic temperature gauge readings that fluctuate wildly or remain stuck at minimum/maximum positions
• Poor fuel economy and excessive black smoke due to improper fuel-to-air mixture calculations
• Engine derate mode activation in severe cases, limiting maximum RPM to protect the engine

Potential Causes

The most common technical failures triggering Code 118 on used SH220LC-6 excavators include:

• Coolant temperature sensor failure due to internal resistance degradation (common after 5,000+ operating hours)
• Damaged or corroded wiring harness at known rub points near the engine block mounting brackets
• Connector corrosion at the sensor plug, particularly on machines exposed to wet or coastal environments
• Open circuit conditions caused by broken wires in the harness between the sensor and ECM
• ECM ground circuit issues affecting multiple sensor readings simultaneously
• Contaminated coolant causing sensor element coating and false readings

How to Troubleshoot and Fix Code 118

Step 1: Visual Inspection Begin by locating the coolant temperature sensor on the engine block (typically near the thermostat housing). Inspect the sensor connector for corrosion, moisture intrusion, or damaged pins. On used excavators, check the wiring harness routing for signs of chafing against metal edges, particularly where the harness passes near engine mounts or vibration points.

Step 2: Electrical Testing Using a digital multimeter, disconnect the sensor and measure resistance across the sensor terminals. At 20°C (68°F), resistance should read approximately 2,000-3,000 ohms (consult your service manual for exact specifications). Test the harness continuity from the sensor connector back to the ECM, checking for resistance below 5 ohms. Measure supply voltage at the connector with ignition on—you should see approximately 5 volts reference voltage from the ECM.

Step 3: Component Replacement and Verification If sensor resistance is out of specification or the harness shows high resistance/open circuits, replace the faulty component. For used machines, always apply dielectric grease to connector pins before reassembly to prevent future corrosion. Clear the fault code using Sumitomo diagnostic software or a compatible scan tool, then run the engine through a complete warm-up cycle to verify the repair.

Disclaimer: This guide provides general troubleshooting information. Always consult the manufacturer's service manual for your specific machine serial number and consider professional diagnostic assistance for complex electrical issues or if you're unfamiliar with high-voltage systems.