Sumitomo SH220LC-6 Fault Code 687: Complete Diagnostic Guide

What is Sumitomo SH220LC-6 Fault Code 687?

Fault Code 687 on the Sumitomo SH220LC-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 ECT (Engine Coolant Temperature) sensor system.

This diagnostic trouble code is generated when the Engine Control Module (ECM) receives coolant temperature readings outside the acceptable voltage range (typically 0.2-4.8V). The ECT sensor is critical for proper fuel injection timing, idle speed control, and protecting the engine from overheating conditions. On the SH220LC-6's diesel engine management system, accurate coolant temperature data directly affects combustion efficiency and emission controls. Ignoring this code can lead to poor fuel economy, rough idle, and potential engine damage from improper thermal management.

Common Symptoms

When Code 687 is active on your SH220LC-6, operators typically experience:

• Check engine warning light illuminated on the instrument cluster, sometimes accompanied by audible alerts
• Hard starting conditions, especially during cold weather, as the ECM cannot properly adjust fuel delivery
• Rough or unstable idle speed with RPM fluctuations due to incorrect temperature compensation
• Cooling fan running continuously at high speed, regardless of actual engine temperature
• Reduced engine performance or derate mode activation as a protective measure against perceived overheating

Potential Causes

The most common technical failures triggering Code 687 on used SH220LC-6 excavators include:

• Failed ECT sensor element due to internal resistance degradation (common after 5,000+ operating hours)
• Damaged wiring harness near the engine block where vibration causes wire insulation breakdown
• Corroded connector pins at the sensor plug, especially on machines operating in wet or coastal environments
• Chafed wiring at the harness routing point behind the fuel filter assembly (known wear location on this model)
• Poor ground connection at the ECM or sensor ground circuit
• ECM internal fault (rare, but possible on high-hour machines with electrical system history)

How to Troubleshoot and Fix Code 687

Step 1: Visual Inspection Begin by inspecting the ECT sensor located on the engine block near the thermostat housing. Check for coolant leaks, corrosion on the two-wire connector, and physical damage. On used excavators, carefully examine the wiring harness for rubbing points against the engine block or fuel lines—a common failure mode on the SH220LC-6.

Step 2: Electrical Testing Disconnect the ECT sensor connector 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 your service manual for exact specifications). Test harness continuity from the sensor connector back to the ECM pins, checking for opens or shorts to ground.

Step 3: Live Voltage Check With the ignition on and sensor disconnected, measure the reference voltage at the harness connector—should be approximately 5V. If voltage is absent, trace the circuit toward the ECM for breaks. If present, reconnect the sensor and measure signal voltage while monitoring temperature; voltage should decrease smoothly as temperature rises.

Step 4: Connector Service Clean all connector pins with electrical contact cleaner and apply dielectric grease to prevent future corrosion. This step is particularly important on used machines where connector deterioration is common.

Step 5: Component Replacement If testing confirms sensor failure, replace with an OEM or quality aftermarket ECT sensor. Always use new sealing washers to prevent coolant leaks. After replacement, clear codes using diagnostic software 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 serial number and consider professional diagnostic assistance for complex electrical issues or if you're unfamiliar with high-voltage systems.