Sumitomo SH360HD-6 Fault Code 1655: Complete Diagnostic Guide

What is Sumitomo SH360HD-6 Fault Code 1655?

Fault Code 1655 indicates a malfunction in the engine coolant temperature sensor circuit, specifically detecting an abnormal voltage signal or open circuit condition in the ECT (Engine Coolant Temperature) sensor system. This code triggers when the ECM (Engine Control Module) receives a signal outside the normal operating range of 0.5-4.5 volts from the coolant temperature sensor.

This fault is critical for the SH360HD-6 because the ECM relies on accurate coolant temperature data to control fuel injection timing, idle speed, and engine protection systems. When this sensor fails, the engine may enter a derate mode or default to a fixed temperature value, compromising performance and potentially causing long-term engine damage through improper fuel management.

Common Symptoms

• Yellow or amber engine warning light illuminated on the instrument cluster
• Engine running rough at cold start or failing to reach proper operating temperature
• Black smoke from exhaust due to incorrect fuel mixture compensation
• Higher than normal fuel consumption as the ECM defaults to rich fuel settings
• Cooling fan running continuously even when engine temperature is normal
• Reduced hydraulic performance during initial operation before engine warms up

Potential Causes

The most common technical failures triggering Code 1655 on used SH360HD-6 excavators include:

• Damaged or corroded wiring harness at the sensor connector, particularly where the harness routes near the engine block (known rub point on this model)
• Failed coolant temperature sensor due to internal resistance degradation after 5,000+ operating hours
• Corroded pins or moisture intrusion in the ECT sensor connector (common in machines operating in wet/muddy conditions)
• Open circuit in the sensor ground wire between the sensor and ECM
• ECM internal fault (less common, but possible in high-hour machines)
• Coolant contamination causing sensor element coating and false readings

How to Troubleshoot and Fix Code 1655

Step 1: Visual Inspection Locate the coolant temperature sensor on the engine block (typically on the thermostat housing). Inspect the wiring harness for visible damage, particularly where it passes near sharp edges or moving components. Check the connector for corrosion, bent pins, or moisture. On used excavators, pay special attention to harness wear points—this is the most common failure on SH360HD-6 models with over 6,000 hours.

Step 2: Electrical Testing Disconnect the sensor and use a digital multimeter to check sensor resistance. At 68°F (20°C), resistance should read approximately 2,400-2,700 ohms. Test the harness voltage at the connector with ignition on: you should see 5 volts reference voltage from the ECM. Check continuity of the ground circuit to the ECM—any resistance above 1 ohm indicates a wiring problem.

Step 3: Signal Testing and Replacement Using Sumitomo diagnostic software or a compatible scan tool, monitor live sensor data while warming the engine. The voltage should decrease smoothly from approximately 4.5V (cold) to 0.5V (hot). Erratic readings indicate sensor failure. Replace the ECT sensor with OEM or quality aftermarket parts, applying proper thread sealant. Clear codes and verify repair by monitoring temperature correlation between sensor reading and actual coolant temperature.

Step 4: Verify Repair After replacement, run the machine through a complete heat cycle and verify the cooling fan engages at proper temperature (approximately 195°F). Re-check for code reoccurrence after 1 hour of operation.

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