Sumitomo SH210LC-5LR Fault Code 108: Complete Diagnostic Guide

What is Sumitomo SH210LC-5LR Fault Code 108?

Fault Code 108 on the Sumitomo SH210LC-5LR indicates a malfunction in the Engine Coolant Temperature (ECT) Sensor circuit, specifically detecting an abnormally high voltage signal or open circuit condition. This diagnostic trouble code (DTC) is generated when the Engine Control Module (ECM) receives a voltage reading outside the expected range from the coolant temperature sensor, typically above 4.5 volts.

The ECT sensor plays a critical role in engine management by monitoring coolant temperature and sending real-time data to the ECM. This information directly influences fuel injection timing, idle speed control, and engine protection protocols. On used excavators like the SH210LC-5LR, this sensor's accuracy is essential for preventing overheating and maintaining optimal hydraulic system performance during demanding operations.

Common Symptoms

When Code 108 is active on your Sumitomo excavator, operators typically experience:

• Check Engine Light or malfunction indicator illuminated on the instrument panel
• Hard starting conditions, especially when the engine is cold, due to incorrect fuel mixture calculations
• Rough idling or unstable engine RPM as the ECM defaults to failsafe temperature values
• Reduced engine power or derate mode activation to protect against perceived overheating
• Cooling fan running continuously at maximum speed regardless of actual engine temperature

Potential Causes

The most common technical reasons for Code 108 appearing on used SH210LC-5LR excavators include:

• Open circuit in the ECT sensor wiring harness, often caused by wire breaks near flex points around the engine block
• Failed ECT sensor with internal resistance breakdown (common after 5,000+ operating hours)
• Corroded or loose connector pins at the sensor plug, particularly on machines exposed to moisture or harsh environments
• Damaged wiring insulation from rubbing against engine components or heat shields
• ECM internal fault (rare, but possible on high-hour machines with electrical system history)
• Improper sensor installation after previous repairs, causing poor thermal contact with coolant passages

How to Troubleshoot and Fix Code 108

Step 1: Visual Inspection Begin by locating the ECT sensor on the engine block (typically near the thermostat housing). Inspect the wiring harness from sensor to ECM for visible damage, chafing, or burns. Check the connector for corrosion, bent pins, or moisture intrusion—common issues on used excavators operating in dusty or wet conditions.

Step 2: Electrical Testing Disconnect the ECT sensor connector. Using a digital multimeter, measure resistance across the sensor terminals. A functional sensor should read approximately 2,000-3,000 ohms at room temperature. An open circuit (infinite resistance) or reading outside specification confirms sensor failure. Next, check for voltage supply at the harness connector with ignition on—you should see approximately 5 volts reference voltage from the ECM.

Step 3: Harness Continuity Check With the sensor disconnected and ignition off, test continuity between the sensor connector pins and corresponding ECM terminals (consult service manual for pin assignments). Resistance should be less than 1 ohm. High resistance indicates damaged wiring requiring repair or replacement.

Step 4: Component Replacement If testing confirms sensor failure, replace with an OEM-equivalent ECT sensor using proper thread sealant. For used machines, always apply dielectric grease to connector pins before reassembly to prevent future corrosion. Clear codes using diagnostic software and verify repair by monitoring live coolant temperature data during warm-up cycle.

Disclaimer: This guide provides general troubleshooting information. Always consult the official Sumitomo service manual for your specific serial number and consider professional diagnostic assistance for complex electrical issues or if unfamiliar with excavator systems.