What is Sumitomo SH200-5 Fault Code 0108?

Fault Code 0108 on the Sumitomo SH200-5 excavator indicates a Coolant Temperature Sensor Circuit Malfunction. This code triggers when the Engine Control Module (ECM) detects an abnormal voltage signal from the coolant temperature sensor, typically reading values outside the expected range of 0.5-4.5 volts.

The coolant temperature sensor plays a critical role in the SH200-5's Isuzu engine management system by monitoring engine operating temperature. The ECM uses this data to adjust fuel injection timing, idle speed, and activate cooling fan cycles. When this sensor circuit fails, the engine control system cannot properly regulate temperature-dependent functions, potentially leading to poor fuel economy, overheating risks, or inadequate engine warm-up. For used excavators, this is particularly concerning as prolonged operation with incorrect temperature readings can accelerate engine wear and cause serious damage.

Common Symptoms

When Code 0108 is active on your SH200-5, you may experience:

• Check Engine Warning Light illuminated on the instrument panel
• Hard starting or extended cranking time, especially in cold conditions
• Engine running excessively rich or lean, producing black smoke or rough idle
• Cooling fan running continuously even when engine is cold
• Reduced engine performance and increased fuel consumption
• Engine may enter derate mode or fail to reach optimal operating temperature

Potential Causes

Several factors commonly trigger this fault code in used Sumitomo excavators:

• Faulty coolant temperature sensor due to internal resistance drift or element failure (common after 5,000+ operating hours)
• Damaged or corroded wiring harness at connector pins, particularly where the harness runs near the exhaust manifold
• Broken or frayed sensor wires caused by vibration or rubbing against engine components—a known wear point on SH200-5 models
• Corroded electrical connectors from coolant leaks or moisture intrusion in the engine bay
• ECM internal fault or poor ground connection at the control module
• Short circuit to ground or power in the sensor circuit wiring

How to Troubleshoot and Fix Code 0108

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 around the sensor base, and ensure the electrical connector is firmly seated. On used machines, examine the entire wiring harness for insulation cracks, heat damage, or abrasion points where wires contact metal surfaces.

Step 2: Electrical Testing Disconnect the sensor connector and use a digital multimeter to measure sensor resistance. At 68°F (20°C), resistance should read approximately 2,000-3,000 ohms; at 176°F (80°C), it should drop to 200-400 ohms. Compare readings to Sumitomo specifications. Next, check circuit voltage with the key on, engine off—you should see approximately 5 volts at the harness connector from the ECM.

Step 3: Circuit and Ground Testing With the sensor disconnected, check for continuity between sensor signal wire and ground (should be infinite resistance/open circuit). Test the ground circuit for less than 1 ohm resistance. For used excavators, pay special attention to corrosion on connector terminals—clean with electrical contact cleaner and dielectric grease before reassembly.

Step 4: Component Replacement If sensor readings are out of specification, replace the coolant temperature sensor with a genuine Sumitomo or OEM-equivalent part. If sensor tests good but code persists, inspect ECM connections and consider advanced diagnostics with Sumitomo diagnostic software to rule out controller issues.

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Disclaimer: This guide provides general troubleshooting information. Always consult your Sumitomo service manual and consider professional diagnosis for complex electrical issues. Improper repairs may cause equipment damage or safety hazards.