Sumitomo SH220LC-6 Fault Code 1404: Technical Guide

What is Sumitomo SH220LC-6 Fault Code 1404?

Fault Code 1404 on the Sumitomo SH220LC-6 indicates a malfunction in the engine coolant temperature sensor circuit or an out-of-range coolant temperature reading. This diagnostic trouble code (DTC) is triggered when the Engine Control Module (ECM) detects an abnormal voltage signal from the coolant temperature sensor, typically indicating an open circuit, short circuit, or sensor degradation.

The coolant temperature sensor is critical for the SH220LC-6's engine management system, as it directly influences fuel injection timing, idle speed control, and overheat protection protocols. When this code activates, the ECM may default to a predetermined temperature value, potentially affecting engine performance and fuel efficiency. For used excavators, this fault commonly appears due to sensor wear, corroded connectors, or damaged wiring harnesses—issues that escalate with machine age and operating hours.

Common Symptoms

• Engine warning light illuminated on the instrument cluster, often accompanied by a coolant temperature warning
• Hard starting conditions, especially during cold starts, as the ECM cannot properly adjust fuel delivery
• Rough idle or irregular engine RPM due to incorrect temperature compensation
• Reduced engine power or activation of derate mode as a protective measure
• Cooling fan running continuously at high speed, even when engine temperature appears normal

Potential Causes

• Faulty coolant temperature sensor due to internal resistance drift or element failure (common in high-hour machines)
• Damaged or corroded wiring harness connecting the sensor to the ECM, particularly at known rub points near the engine block
• Corroded or loose electrical connectors at the sensor terminal—moisture intrusion is common in older excavators
• ECM internal fault or corrupted calibration data (less common but possible in used equipment)
• Low coolant levels causing sensor exposure to air, resulting in erratic readings
• Aftermarket or incorrect sensor replacement with incompatible resistance specifications

How to Troubleshoot and Fix Code 1404

Step 1: Visual Inspection Begin with a thorough visual examination of the coolant temperature sensor located on the engine block (typically near the thermostat housing). Check for physical damage, coolant leaks around the sensor base, and verify adequate coolant levels. Inspect the wiring harness from sensor to ECM for abrasion, particularly where it contacts metal surfaces or passes through grommets—a common failure point on used SH220LC-6 models.

Step 2: Electrical Testing Disconnect the sensor connector and use a digital multimeter to measure sensor resistance. At room temperature (68°F/20°C), resistance should typically read between 2,000-3,000 ohms (consult service manual for exact specifications). Test the harness by measuring voltage supply from the ECM (should read approximately 5 volts) and check for continuity between sensor ground and ECM ground. Any reading outside specifications indicates wiring faults or ECM issues.

Step 3: Component Replacement and Verification If the sensor tests faulty, replace it with an OEM-equivalent sensor matching Sumitomo specifications. For used excavators, always apply dielectric grease to connector terminals to prevent future corrosion. After replacement, clear the fault code using diagnostic software (Sumitomo-compatible scan tool) and perform a cold-start test cycle to verify proper operation. Monitor live coolant temperature data to ensure readings correspond with actual engine temperature.

Disclaimer: This guide provides general troubleshooting information. Always consult the official Sumitomo service manual for your specific machine serial number and consider professional diagnostic assistance for complex electrical issues or ECM programming requirements.