Sumitomo SH300-6 Fault Code 1404: Complete Diagnostic Guide

What is Sumitomo SH300-6 Fault Code 1404?

Fault Code 1404 on the Sumitomo SH300-6 excavator indicates a malfunction in the engine coolant temperature sensor circuit or an abnormal coolant temperature reading detected by the ECM (Engine Control Module). This code specifically relates to the engine's thermal management system, where the ECM receives voltage signals from the coolant temperature sensor to regulate fuel injection timing, idle speed, and engine protection protocols.

This fault is critical for the SH300-6's performance because the engine relies on accurate temperature data to prevent overheating, optimize fuel efficiency, and trigger protective shutdown sequences. When this code activates, the ECM may default to a preset temperature value, potentially causing improper engine operation or reduced hydraulic performance.

Common Symptoms

When Code 1404 is active on your Sumitomo SH300-6, operators typically experience:

• Engine warning light or check engine light illuminated on the dash panel
• Hard starting or extended cranking time, especially in cold conditions
• Black smoke from the exhaust due to incorrect fuel-air mixture calculations
• Engine running rough at idle or failure to reach normal operating temperature
• Reduced hydraulic power or slower cycle times as the ECM limits engine output

Potential Causes

The most common technical reasons for Code 1404 appearing on used SH300-6 excavators include:

• Faulty coolant temperature sensor due to internal element degradation (common after 5,000+ operating hours)
• Corroded or loose wiring connectors at the sensor harness connection point
• Damaged sensor harness from rubbing against engine components or heat exposure near the turbocharger
• Low coolant level causing the sensor to read air instead of coolant temperature
• Failed ECM or internal circuit board corrosion (rare but possible in high-hour machines)
• Aftermarket sensor incompatibility if previous repairs used non-OEM parts

How to Troubleshoot and Fix Code 1404

Step 1: Visual Inspection Begin by checking the coolant level in the radiator and overflow tank. On used excavators, inspect the sensor wiring harness from the ECM to the coolant temperature sensor for visible damage, chafing, or connector corrosion. The sensor is typically located on the engine block near the thermostat housing.

Step 2: Electrical Testing Using a digital multimeter, disconnect the coolant temperature sensor connector and 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 the harness voltage with the key on, engine off—you should see approximately 5 volts supply from the ECM.

Step 3: Component Replacement and Verification If resistance values are out of specification or the sensor shows open or short circuit readings, replace the coolant temperature sensor with a genuine Sumitomo or OEM-equivalent part. For used excavators with over 8,000 hours, consider replacing the sensor pigtail connector simultaneously, as corrosion often occurs internally. After replacement, clear the fault code using diagnostic software and monitor for recurrence during a complete warm-up cycle.

Disclaimer: This guide provides general troubleshooting steps. Always consult a certified Sumitomo technician or the official service manual for your specific machine serial number before performing repairs. Improper diagnostics may cause additional damage.