Sumitomo SH360HD-6 Fault Code 335: Complete Diagnostic Guide

What is Sumitomo SH360HD-6 Fault Code 335?

Fault Code 335 on the Sumitomo SH360HD-6 excavator indicates a malfunction in the Engine Coolant Temperature (ECT) Sensor Circuit, specifically detecting an abnormally high voltage signal or open circuit condition. This code is triggered when the Engine Control Module (ECM) receives a voltage reading from the coolant temperature sensor that exceeds the normal operating range (typically above 4.5-4.8 volts), suggesting either a faulty sensor, damaged wiring, or poor electrical connections.

The ECT sensor plays a critical role in engine performance management on the SH360HD-6's diesel engine. It directly influences fuel injection timing, idle speed control, and cooling fan activation. When this sensor circuit fails, the ECM enters a default "limp mode" using predetermined temperature values, which can reduce engine efficiency and potentially cause overheating if the actual coolant temperature isn't being monitored accurately.

Common Symptoms

When Code 335 is active on your SH360HD-6, you may experience:

• Check Engine Light or warning lamp illuminated on the instrument cluster
• Cooling fan running continuously at high speed, even during cold starts
• Difficult cold starting or extended cranking time due to improper fuel delivery calculations
• Reduced engine power or restricted RPM as the ECM implements protective derate measures
• Erratic temperature gauge readings showing maximum temperature regardless of actual engine condition

Potential Causes

The most common technical reasons for Code 335 on used Sumitomo excavators include:

• Open circuit in ECT sensor wiring harness – particularly at flex points near the engine mount where vibration causes wire breakage
• Failed ECT sensor with internal resistance breakdown (common after 5,000+ operating hours)
• Corroded or loose connector pins at the sensor plug or ECM connection points
• Damaged sensor ground wire creating voltage reference issues
• Chafed wiring harness rubbing against the engine block or hydraulic lines (known issue on SH360HD-6 models)
• ECM internal fault (rare, but possible on 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 (typically near the thermostat housing). Check for physical damage, coolant leaks around the sensor base, and examine the wiring harness for obvious chafing, cuts, or heat damage. On used excavators, pay special attention to wire routing near moving components.

Step 2: Electrical Testing Using a digital multimeter, disconnect the ECT sensor connector and measure resistance across the sensor terminals. At room temperature (68°F/20°C), resistance should read approximately 2,000-3,000 ohms (consult service manual for exact specifications). If reading is infinite (open circuit) or zero, replace the sensor.

Step 3: Circuit Continuity Check With the sensor disconnected, check voltage at the harness connector. You should see approximately 5 volts reference voltage from the ECM. Also verify ground continuity (less than 1 ohm resistance to chassis ground). Repair or replace harness sections showing high resistance or voltage drops.

Step 4: Connector Service Clean all connector terminals with electrical contact cleaner and inspect for corrosion or bent pins—extremely common on machines operating in harsh environments. Apply dielectric grease to prevent future moisture intrusion.

Step 5: Clear Code and Verify After repairs, clear the fault code using diagnostic software and operate the machine through a complete heat cycle to confirm the repair.

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