Sumitomo SH260LC-6 Fault Code 1655: Technical Guide

What is Sumitomo SH260LC-6 Fault Code 1655?

Fault Code 1655 on the Sumitomo SH260LC-6 indicates a malfunction in the engine coolant temperature sensor circuit, specifically detecting an abnormal voltage signal or out-of-range reading from the coolant temperature sensor to the Engine Control Module (ECM).

This diagnostic trouble code (DTC) triggers when the ECM detects that the coolant temperature sensor is sending voltage readings outside the manufacturer's specified parameters—typically either too high (open circuit) or too low (short circuit). The coolant temperature sensor plays a critical role in engine performance management, controlling fuel injection timing, idle speed, and emission controls. On used excavators like the SH260LC-6, this sensor's data directly influences the machine's ability to prevent overheating and maintain optimal operating temperatures during demanding hydraulic operations.

Common Symptoms

When Code 1655 is active on your Sumitomo SH260LC-6, operators typically experience:

• Check Engine Light or warning lamp illuminated on the instrument cluster
• Hard starting conditions, especially during cold starts, as the ECM cannot properly adjust fuel delivery
• Rough idling or irregular engine RPM fluctuations
• Cooling fan running continuously at maximum speed regardless of actual engine temperature
• Reduced engine power or derate mode activation to protect the engine from potential overheating damage

Potential Causes

The most common technical reasons for Code 1655 appearing on used SH260LC-6 excavators include:

• Failed coolant temperature sensor due to internal resistance drift or element degradation (common after 5,000+ operating hours)
• Damaged wiring harness or corroded connectors between the sensor and ECM, particularly at harness routing points near the engine block where vibration and heat cause wear
• Broken or frayed sensor wiring at known rub points along the valve cover or fuel injection pump mounting areas
• Poor ground connection at the sensor or ECM ground terminals
• Contaminated coolant causing sensor element fouling or coating
• ECM internal fault (rare, but possible in high-hour machines)

How to Troubleshoot and Fix Code 1655

Step 1: Visual Inspection Begin by conducting a thorough visual inspection of the coolant temperature sensor (typically located on the engine block near the thermostat housing). Check the electrical connector for corrosion, moisture intrusion, bent pins, or physical damage. On used excavators, pay special attention to connector seals that may have degraded over time.

Step 2: Resistance Testing Disconnect the sensor and use a digital multimeter to measure resistance across the sensor terminals. At room temperature (68°F/20°C), resistance should typically read between 2,000-3,000 ohms (consult your service manual for exact specifications). Test again with the engine at operating temperature—resistance should decrease to approximately 200-400 ohms. Values significantly outside this range indicate sensor failure.

Step 3: Wiring Harness Verification Inspect the sensor wiring harness from the sensor to the ECM connector. Check for damaged insulation, particularly where the harness contacts metal surfaces or passes near moving components. Use your multimeter to test for continuity in each wire and verify there are no shorts to ground. Test voltage supply from the ECM—you should see approximately 5 volts at the sensor connector with the key on, engine off.

Step 4: Connector and Ground Cleaning For used machinery, clean all connector terminals with electrical contact cleaner and apply dielectric grease to prevent future corrosion. Verify the ground connection at both the sensor mounting point and ECM chassis ground—remove, clean with a wire brush, and reinstall securely.

Step 5: Component Replacement If testing confirms sensor failure, replace with an OEM-equivalent coolant temperature sensor. After installation, clear the fault code using diagnostic software compatible with Sumitomo systems and perform a test cycle to verify repair.

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Disclaimer: This guide provides general troubleshooting information for experienced technicians. Always consult the official Sumitomo service manual for your specific machine serial number and software version. If you're uncomfortable performing electrical diagnostics, contact a certified Sumitomo technician or heavy equipment repair specialist to prevent further damage to your excavator's electrical system.