Sumitomo SH300-6 Fault Code 335: Complete Diagnostic Guide

What is Sumitomo SH300-6 Fault Code 335?

Fault Code 335 on the Sumitomo SH300-6 excavator indicates a malfunction in the Engine Coolant Temperature (ECT) Sensor Circuit, specifically detecting an abnormal voltage signal or open circuit condition. This diagnostic trouble code (DTC) is triggered when the Engine Control Module (ECM) receives a voltage reading outside the acceptable range from the coolant temperature sensor, typically above 4.8 volts or below 0.2 volts.

The ECT sensor plays a critical role in the SH300-6's engine management system by monitoring coolant temperature and allowing the ECM to adjust fuel injection timing, idle speed, and emissions controls. When this sensor circuit fails, the engine may run inefficiently, experience cold-start difficulties, or enter a protective derate mode to prevent potential damage.

Common Symptoms

When Code 335 is active on your Sumitomo SH300-6, operators typically experience:

• Check Engine Light or malfunction indicator lamp illuminated on the instrument cluster
• Hard starting or extended cranking time, especially in cold conditions
• Rough idle or irregular engine RPM fluctuations during warm-up
• Reduced engine power or automatic derate limiting maximum throttle response
• Cooling fan running continuously at high speed regardless of actual engine temperature

Potential Causes

The most common technical reasons for Code 335 on used SH300-6 excavators include:

• Faulty ECT sensor with internal resistance drift or element failure (common after 5,000+ operating hours)
• Damaged wiring harness particularly at the firewall pass-through where vibration causes insulation wear
• Corroded or loose connector pins at the sensor plug due to coolant leaks or moisture intrusion
• Broken or shorted sensor ground wire (often caused by previous repair work or harness routing issues)
• ECM internal fault affecting the 5-volt reference circuit (rare, but documented in high-hour machines)

How to Troubleshoot and Fix Code 335

Step 1: Visual Inspection Begin by inspecting the ECT sensor located on the engine block near the thermostat housing. Check for coolant leaks, corrosion on the electrical connector, and physical damage to the wiring harness. On used excavators, pay special attention to harness routing where it contacts frame members or vibrates against metal surfaces.

Step 2: Electrical Testing Disconnect the sensor connector and use a digital multimeter to check sensor resistance. At 68°F (20°C), resistance should read approximately 2,000-3,000 ohms. Test the harness voltage with ignition on, engine off—you should measure approximately 5 volts at the signal wire. Check for continuity to ground on the ground circuit (should read less than 1 ohm).

Step 3: Component Replacement If sensor resistance is out of specification or harness voltage is incorrect, replace the faulty component. For used machines, always apply dielectric grease to connector pins and secure harnesses away from heat sources and moving parts. Clear the code using Sumitomo diagnostic software or a compatible scan tool, then perform a test cycle to verify the repair.

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