Sumitomo SH260LC-6 Fault Code 1404: Complete Diagnostic Guide

What is Sumitomo SH260LC-6 Fault Code 1404?

Fault Code 1404 on the Sumitomo SH260LC-6 excavator indicates a malfunction in the engine coolant temperature (ECT) sensor circuit or an out-of-range coolant temperature reading. This diagnostic trouble code (DTC) is triggered when the electronic control module (ECM) detects abnormal voltage signals from the coolant temperature sensor, typically indicating an open circuit, short circuit, or sensor failure.

The ECT sensor plays a critical role in engine management by monitoring coolant temperature and sending voltage signals to the ECM. This data directly affects fuel injection timing, idle speed control, and engine protection systems. On used excavators like the SH260LC-6, this code can lead to improper engine operation, reduced performance, and potential overheating if ignored.

Common Symptoms

When Code 1404 is active on your Sumitomo SH260LC-6, you may experience:

• Check engine light or malfunction indicator lamp illuminated on the dashboard
• Engine running in limp mode with reduced power output and limited RPM
• Difficulty starting, especially during cold weather conditions
• Erratic or stuck temperature gauge readings on the instrument cluster
• Cooling fans running continuously at maximum speed, even when engine is cold
• Rough idle or poor fuel economy due to incorrect fuel mapping

Potential Causes

Several factors can trigger Code 1404 on used Sumitomo excavators:

• Failed coolant temperature sensor due to internal resistance breakdown or contamination
• Damaged wiring harness between the ECT sensor and ECM, particularly at flex points near the engine block
• Corroded or loose electrical connectors at the sensor or ECM—common in machines exposed to harsh environments
• Short to ground in the sensor signal wire caused by harness chafing against metal surfaces
• Open circuit from broken wires inside the insulation (invisible damage common in older machines)
• ECM internal fault affecting the sensor input circuit (rare but possible in high-hour machines)

How to Troubleshoot and Fix Code 1404

Step 1: Visual Inspection Begin by locating the ECT sensor on the engine block (typically near the thermostat housing). Inspect the sensor connector for corrosion, moisture, or bent pins. On used excavators, check the wiring harness for signs of rubbing, cracking, or heat damage along its entire length to the ECM.

Step 2: Test Sensor Resistance Disconnect the sensor connector and use a digital multimeter to measure resistance across the sensor terminals. At room temperature (68°F/20°C), resistance should typically read 2,000-3,000 ohms (consult your service manual for exact specifications). If readings are infinite (open) or near zero (shorted), replace the sensor.

Step 3: Check Circuit Voltage With the ignition on and sensor disconnected, measure voltage at the harness connector (ECM side). You should see approximately 5 volts on the signal wire. No voltage indicates a wiring issue or ECM problem. Also check for continuity between the sensor ground and chassis ground.

Step 4: Inspect for Intermittent Faults Wiggle the harness while monitoring resistance or voltage—this reveals intermittent connections common in used machines. Pay special attention to connector seals and areas where the harness passes through grommets or near hot exhaust components.

Step 5: Clear Code and Verify After repairs, clear the fault code using diagnostic software compatible with Sumitomo systems. Run the engine through temperature cycles and monitor for code recurrence before returning the excavator to service.

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Disclaimer: This guide provides general troubleshooting information for Code 1404. Always consult the official Sumitomo service manual for your specific machine serial number and seek assistance from certified technicians for complex electrical diagnostics or if you're unsure about any procedure.