Sumitomo SH380LHD-6 Fault Code 118: Meaning and Fix Guide

What is Sumitomo SH380LHD-6 Fault Code 118?

Fault Code 118 on the Sumitomo SH380LHD-6 indicates a malfunction in the engine coolant temperature (ECT) sensor circuit or an abnormal coolant temperature reading detected by the ECM (Engine Control Module). This code specifically signals that the ECT sensor is either sending voltage values outside the normal operating range or has detected coolant temperatures exceeding safe operational limits.

The engine coolant temperature sensor plays a critical role in the SH380LHD-6's diesel engine management system. It provides real-time temperature data to the ECM, which uses this information to adjust fuel injection timing, control engine warm-up cycles, and prevent overheating damage. When this sensor fails or provides erratic readings, the excavator's performance, fuel efficiency, and engine longevity are all compromised.

Common Symptoms

When Code 118 is active on your Sumitomo excavator, operators typically experience:

• Check Engine Light or malfunction indicator illuminated on the instrument panel
• Reduced engine power or activation of derate mode, limiting machine productivity
• Hard starting when the engine is cold, as the ECM cannot properly manage cold-start fuel enrichment
• Cooling fan running continuously at high speed, even when engine temperature appears normal
• Erratic temperature gauge readings that fluctuate abnormally or display unrealistic values

Potential Causes

Several technical issues commonly trigger Code 118 in used SH380LHD-6 excavators:

• Failed ECT sensor due to internal element degradation or contamination from coolant additives
• Damaged wiring harness between the sensor and ECM, particularly at flex points near the engine mount where vibration causes wire fatigue
• Corroded or loose electrical connectors at the sensor or ECM terminals, common in machines exposed to harsh environments
• Shorted or open circuit in the sensor signal wire caused by harness chafing against engine components
• Low coolant level or air pockets in the cooling system creating false high-temperature readings
• ECM internal fault affecting the temperature monitoring circuit (less common but possible in high-hour machines)

How to Troubleshoot and Fix Code 118

Step 1: Visual Inspection Begin by inspecting the ECT sensor location (typically on the engine block or cylinder head). Check for physical damage, coolant leaks around the sensor base, and verify the electrical connector is fully seated without corrosion. On used excavators, examine the wiring harness along its entire length for abrasion points, especially where it contacts the engine block or routing brackets.

Step 2: Electrical Testing Disconnect the ECT sensor connector and use a digital multimeter to measure resistance across the sensor terminals. Compare readings to manufacturer specifications (typically 2,000-3,000 ohms at room temperature, decreasing as temperature rises). Check for continuity in the signal wire from sensor to ECM and verify the ground circuit has less than 0.5 ohms resistance.

Step 3: Live Data Analysis Using Sumitomo diagnostic software or a compatible scan tool, monitor live ECT sensor voltage while the engine warms up. Normal readings should show smooth voltage decrease from approximately 4-5 volts (cold) to 0.5-1.5 volts (operating temperature). Erratic fluctuations or stuck readings indicate sensor failure.

Step 4: Component Replacement If testing confirms sensor failure, replace the ECT sensor with a genuine Sumitomo part. For used excavators, always replace the sensor connector pigtail simultaneously, as connector terminals often suffer heat damage. Apply dielectric grease to the new connector to prevent future corrosion. After replacement, clear codes and perform a test cycle.

Disclaimer: This guide provides general troubleshooting information. Always consult the official Sumitomo service manual for your specific machine serial number and consider professional diagnostic assistance for complex electrical issues or if you lack proper diagnostic equipment.