Sumitomo SH240-6 Fault Code 118: Complete Diagnostic Guide

What is Sumitomo SH240-6 Fault Code 118?

Fault Code 118 on the Sumitomo SH240-6 excavator indicates a malfunction in the engine coolant temperature sensor circuit or an abnormal engine coolant temperature reading. This code is triggered when the Engine Control Module (ECM) detects voltage signals outside the normal operating range from the coolant temperature sensor, typically indicating either sensor failure, wiring issues, or genuine overheating conditions.

This fault is critical for the SH240-6's performance because the ECM relies on accurate coolant temperature data to manage fuel injection timing, engine protection protocols, and hydraulic system efficiency. When this sensor fails, the machine may enter a protective derate mode to prevent catastrophic engine damage, significantly reducing productivity on the jobsite.

Common Symptoms

When Code 118 is active on your Sumitomo SH240-6, operators typically experience:

• Engine warning light illuminated on the instrument panel, often accompanied by an audible alarm
• Reduced engine power or automatic derate to idle speed, especially if the ECM assumes overheating
• Difficulty starting the engine, particularly in cold weather conditions
• Erratic temperature gauge readings that fluctuate rapidly or show unrealistic values
• Black smoke from exhaust due to improper fuel mixture compensation

Potential Causes

For used Sumitomo SH240-6 excavators, the most common causes of Code 118 include:

• Failed coolant temperature sensor due to age-related degradation or thermal cycling stress
• Damaged wiring harness near the engine block where vibration and heat cause insulation breakdown
• Corroded or loose electrical connectors at the sensor or ECM connection points
• Shorted sensor ground wire making contact with the engine block or frame
• Low coolant levels causing genuine overheating and triggering legitimate high-temperature readings
• ECM internal faults (less common) affecting the temperature sensor input circuit

How to Troubleshoot and Fix Code 118

Step 1: Visual Inspection Begin by inspecting the coolant temperature sensor located on the engine block near the thermostat housing. Check for physical damage, coolant leaks, or corrosion on the sensor body and connector. On used excavators, examine the wiring harness for chafing points where it contacts the engine or frame—this is a notorious failure point on the SH240-6.

Step 2: Electrical Testing Using a digital multimeter, disconnect the sensor and measure its resistance. At 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 the ECM. Measure voltage at the sensor connector with the key on, engine off—you should see approximately 5 volts reference voltage from the ECM.

Step 3: Component Replacement and Verification If the sensor tests outside specifications or wiring shows open circuits or shorts to ground, replace the faulty component. For used machines, always apply dielectric grease to connector pins to prevent future corrosion. After repairs, clear the fault code using Sumitomo diagnostic software or a compatible scan tool, then run the engine through several heat cycles to verify the fix.

Disclaimer: This guide provides general troubleshooting information. Always consult the official Sumitomo service manual for your specific machine serial number and consider professional diagnostic services for complex electrical issues.