Sumitomo SH210-6 Fault Code 685: Complete Diagnostic Guide

What is Sumitomo SH210-6 Fault Code 685?

Fault Code 685 on the Sumitomo SH210-6 excavator indicates a malfunction in the engine coolant temperature sensor circuit, specifically detecting an abnormal voltage signal or open/short circuit condition in the coolant temperature monitoring system.

This code triggers when the Electronic Control Module (ECM) receives voltage readings outside the expected range (typically 0.5-4.5V) from the engine coolant temperature (ECT) sensor. The ECT sensor is critical for this Isuzu-powered excavator because it directly influences fuel injection timing, idle speed control, and engine protection systems. When this sensor fails, the ECM cannot accurately monitor engine temperature, potentially leading to overheating damage or poor fuel economy on these used machines.

Common Symptoms

When Code 685 is active on your SH210-6, you may experience:

• Check engine light or malfunction warning lamp illuminated on the instrument panel
• Hard starting or extended cranking time, especially during cold starts
• Rough idle or inconsistent engine RPM at operating temperature
• Poor fuel efficiency due to ECM running in default "limp mode" with preset temperature values
• Black smoke from exhaust as the system compensates with a richer fuel mixture

Potential Causes

The most common technical failures causing Code 685 on used Sumitomo excavators include:

• Failed ECT sensor due to internal resistance drift or element failure (common after 5,000+ hours)
• Damaged wiring harness near the thermostat housing where heat and vibration cause insulation breakdown
• Corroded connector pins at the sensor plug—especially prevalent in machines operated in wet or coastal environments
• Broken or frayed wires at known rub points near the engine mount brackets
• ECM internal fault (rare, but possible in high-hour machines with electrical system stress)

How to Troubleshoot and Fix Code 685

Step 1: Visual Inspection Begin by inspecting the ECT sensor located near the thermostat housing on the engine block. Check the wiring harness for visible damage, abrasion, or oil contamination. On used excavators, pay special attention to connector corrosion—disconnect and examine pins for green oxidation or moisture.

Step 2: Electrical Testing Using a digital multimeter, measure the sensor's resistance. At room temperature (68°F/20°C), resistance should read approximately 2,000-3,000 ohms. If readings are infinite (open circuit) or near zero (short circuit), replace the sensor. Also check for supply voltage at the connector—should read approximately 5 volts with key on, engine off.

Step 3: Circuit Continuity Check Test the signal wire and ground wire continuity between the ECT sensor connector and the ECM harness connector. Repair any breaks or shorts. For used machines, consider replacing the entire harness section if insulation is brittle.

Step 4: Clear Code and Verify After repairs, clear the fault code using Sumitomo diagnostic software or a compatible scan tool. Run the engine through temperature cycles and monitor for code reoccurrence.

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Disclaimer: This guide provides general diagnostic information. Always consult the Sumitomo SH210-6 service manual and consider professional diagnosis for complex electrical issues. Improper repairs may cause further damage to engine management systems.