Sumitomo SH360HD-6 Fault Code 685: Complete Diagnostic Guide

What is Sumitomo SH360HD-6 Fault Code 685?

Fault Code 685 on the Sumitomo SH360HD-6 indicates a malfunction in the engine coolant temperature sensor circuit or an abnormal coolant temperature reading detected by the ECM (Engine Control Module). This code specifically points to either a sensor voltage outside acceptable parameters (typically 0.5-4.5V), a circuit short/open, or an actual overheating condition that requires immediate attention.

The coolant temperature sensor is critical for the SH360HD-6's performance because it directly influences fuel injection timing, throttle response, and automatic engine protection systems. When this sensor fails or provides incorrect data, the ECM may trigger derate modes or prevent the machine from operating at full capacity to protect the engine from potential thermal damage.

Common Symptoms

• Engine warning light illuminated on the instrument panel, often accompanied by an audible alarm
• Reduced engine power or automatic derate mode engaging, limiting RPM to approximately 1200-1500
• Hard starting when the engine is cold, or rough idle during warm-up periods
• Cooling fan running continuously at high speed regardless of actual engine temperature
• Erratic temperature gauge readings or gauge stuck at cold/hot extremes

Potential Causes

The most common causes for Code 685 on used SH360HD-6 excavators include:

• Coolant temperature sensor failure due to age, heat cycling, or internal element degradation (common after 5,000+ operating hours)
• Corroded or loose connector pins at the sensor harness connection point near the thermostat housing
• Wiring harness damage from rubbing against the engine block or exhaust manifold—a known wear point on this model
• ECM ground circuit issues causing voltage reference problems
• Actual coolant system problems including low coolant level, air pockets, or thermostat failure creating genuine overheating

How to Troubleshoot and Fix Code 685

Step 1: Visual Inspection Begin by inspecting the coolant temperature sensor located on the engine block near the thermostat housing. Check the wiring harness for visible damage, particularly where it routes near hot engine components. On used excavators, examine connector pins for corrosion, bent terminals, or moisture intrusion—clean with electrical contact cleaner if necessary.

Step 2: Sensor Resistance Testing Disconnect the sensor and use a digital multimeter to measure resistance across the sensor terminals. At 68°F (20°C), resistance should read approximately 2,000-3,000 ohms (consult service manual for exact specifications). Compare readings at different temperatures; resistance should decrease smoothly as temperature increases.

Step 3: Circuit Voltage Check With the sensor disconnected and ignition on, measure voltage at the harness connector. You should see approximately 5V reference voltage from the ECM. If voltage is absent or incorrect, trace the wiring back to the ECM, checking for breaks or shorts to ground.

Step 4: Verify Actual Coolant Condition Before replacing components, confirm the cooling system is functioning properly. Check coolant level, inspect for leaks, verify thermostat operation, and bleed any air from the system. Many used machines develop Code 685 due to neglected cooling system maintenance rather than sensor failure.

Step 5: Component Replacement If diagnostics confirm sensor failure, replace with an OEM or quality aftermarket sensor and apply dielectric grease to connector terminals. Clear the code using Sumitomo diagnostic software or a compatible scan tool and perform a test cycle.

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Disclaimer: This guide provides general troubleshooting information. Always consult the official Sumitomo service manual for your specific machine serial number and consider professional diagnosis for complex electrical issues or if you're unfamiliar with high-voltage systems.