What is Sumitomo SH240-5 Fault Code 108?

Fault Code 108 on the Sumitomo SH240-5 excavator indicates a malfunction in the Engine Water Temperature Sensor circuit or excessively high coolant temperature readings. This diagnostic trouble code (DTC) is triggered when the Engine Control Module (ECM) detects an abnormal voltage signal from the coolant temperature sensor, or when actual coolant temperature exceeds safe operating thresholds (typically above 230°F/110°C).

This code is critical for the SH240-5 because the engine's fuel injection timing, throttle response, and automatic derate functions depend heavily on accurate temperature data. Ignoring this fault can lead to engine overheating, reduced hydraulic performance, and potential catastrophic engine damage, especially in used machines where cooling system maintenance may have been deferred.

Common Symptoms

When Code 108 is active on your Sumitomo SH240-5, you may experience:

• Temperature warning light illuminated on the instrument cluster (typically red or amber)
• Engine power derate or automatic reduction in RPM to protect internal components
• Audible warning alarm sounding continuously during operation
• Overheating gauge reading abnormally high even after short operating periods
• Rough idling or hesitation during hydraulic functions due to ECM compensating for perceived temperature issues

Potential Causes

The most common technical reasons for Code 108 on used SH240-5 excavators include:

• Failed coolant temperature sensor due to internal element degradation (common after 5,000+ operating hours)
• Corroded or damaged wiring harness at the sensor connector, particularly where the harness routes near the exhaust manifold
• Low coolant level causing air pockets that provide false temperature readings
• Defective ECM with internal circuit board issues (less common but possible in older machines)
• Thermostat failure causing genuine overheating that triggers the sensor
• Shorted or open circuit in the temperature sensor wiring due to rubbing against frame components

How to Troubleshoot and Fix Code 108

Step 1: Visual Inspection Begin by checking the coolant level in the radiator and overflow tank when the engine is cold. Inspect the coolant temperature sensor (located on the engine block near the thermostat housing) for physical damage, oil contamination, or corrosion on the connector pins. On used excavators, pay special attention to harness wear points where cables may have rubbed against metal surfaces over thousands of operating hours.

Step 2: Electrical Testing Using a digital multimeter, disconnect the sensor connector and measure the resistance across the sensor terminals. At room temperature (68°F/20°C), resistance should read approximately 2,000-3,000 ohms (consult your service manual for exact specifications). Then check for continuity in the wiring harness from the sensor connector back to the ECM pins. Any reading of infinite resistance indicates an open circuit requiring harness repair or replacement.

Step 3: Live Data Monitoring Connect Sumitomo-compatible diagnostic software (or a universal heavy equipment scanner) to verify real-time coolant temperature readings. Compare the displayed temperature with an infrared thermometer measurement taken directly on the engine block. If readings differ by more than 15°F, replace the sensor. Additionally, check for voltage supply at the sensor connector—it should show approximately 5 volts with the key on, engine off.

Step 4: Component Replacement If diagnostics confirm sensor failure, replace the coolant temperature sensor using OEM or high-quality aftermarket parts. Always apply dielectric grease to connector pins before reassembly to prevent future corrosion—critical for used machines operating in harsh environments. After replacement, clear the fault code using diagnostic software and perform a test cycle to verify the repair.

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Disclaimer: This guide provides general troubleshooting information for Code 108 on Sumitomo SH240-5 excavators. Always consult the manufacturer's service manual and consider professional diagnostic assistance for complex electrical issues or if you're uncomfortable performing these procedures. Improper repairs can cause additional damage or safety hazards.