Sumitomo SH380LHD-6 Fault Code 685: Complete Diagnostic Guide

What is Sumitomo SH380LHD-6 Fault Code 685?

Fault Code 685 on the Sumitomo SH380LHD-6 excavator indicates a malfunction in the engine coolant temperature sensor circuit, specifically reporting an abnormal voltage signal or out-of-range reading from the ECM (Engine Control Module).

This code triggers when the coolant temperature sensor sends voltage readings outside the manufacturer's specified parameters (typically 0.5-4.5V range). The sensor plays a critical role in engine protection by monitoring coolant temperature and adjusting fuel injection timing, idle speed, and triggering thermal protection protocols. On the SH380LHD-6's Isuzu engine platform, accurate temperature monitoring is essential for preventing overheating damage and maintaining optimal hydraulic oil temperature, which directly affects excavator performance and component longevity.

Common Symptoms

When Code 685 is active, operators typically experience:

• Check Engine Light or malfunction indicator illuminated on the instrument panel
• Hard starting or extended cranking time, especially in cold conditions
• Rough idle or unstable engine RPM during warm-up periods
• Reduced engine power or automatic derate mode activation to prevent potential overheating
• Cooling fan running continuously at high speed regardless of actual engine temperature
• Inaccurate temperature gauge readings showing extremely high or low values

Potential Causes

The most common technical failures triggering Code 685 on used SH380LHD-6 excavators include:

• Failed coolant temperature sensor (CTS) due to internal resistance degradation from heat cycling
• Damaged wiring harness near the engine block where vibration causes insulation wear and wire exposure
• Corroded or loose electrical connectors at the sensor or ECM interface, particularly common in machines operating in wet/marine environments
• Shorted or open circuit in the sensor signal wire between the CTS and ECM
• Contaminated coolant creating electrical conductivity issues across sensor terminals
• ECM internal fault (rare) causing incorrect voltage reference supply to the sensor circuit

How to Troubleshoot and Fix Code 685

Step 1: Visual Inspection Begin by inspecting the coolant temperature sensor located on the engine block (typically near the thermostat housing). Check for physical damage, coolant leaks around the sensor base, or corrosion on the electrical connector. On used excavators, examine the wiring harness routing for signs of rubbing against engine components, heat damage from exhaust manifolds, or oil contamination that degrades insulation.

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 (consult service manual for exact specifications). Test circuit continuity from the sensor connector to the ECM and check for shorts to ground. Measure the reference voltage from the ECM (should be approximately 5V with ignition on, sensor disconnected).

Step 3: Component Replacement and Verification If sensor resistance is out-of-specification or wiring shows damage, replace the coolant temperature sensor with an OEM or equivalent part. For used machines with over 5,000 hours, consider replacing the connector pigtail as preventive maintenance against future corrosion issues. Clear the fault code using diagnostic software (Sumitomo SIM or compatible scan tool) and monitor live data to verify the sensor now reads correctly across temperature ranges.

Disclaimer: This guide provides general diagnostic information. Always consult the official Sumitomo service manual for your specific serial number and consider professional diagnosis for complex electrical issues or if problems persist after repairs.