Sumitomo SH350HD-5 Fault Code 335: Complete Diagnostic Guide

What is Sumitomo SH350HD-5 Fault Code 335?

Fault Code 335 on the Sumitomo SH350HD-5 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 registered by the machine's Electronic Control Module (ECM) when the coolant temperature sensor sends voltage readings outside the acceptable operating range (typically above 4.5 volts).

This diagnostic trouble code is critical for the SH350HD-5's performance because the ECT sensor provides essential data for fuel injection timing, engine protection systems, and hydraulic oil temperature management. When this code activates, the ECM defaults to a predetermined temperature value, which can result in suboptimal engine performance, increased fuel consumption, and potential overheating risks if not addressed promptly.

Common Symptoms

Operators experiencing Code 335 on their Sumitomo SH350HD-5 may notice:

• Engine warning light illuminated on the instrument cluster with possible audible alarm
• Hard starting or extended cranking time, especially in cold conditions
• Rough idle and irregular engine RPM fluctuations during warm-up
• Cooling fan running continuously at high speed regardless of actual engine temperature
• Reduced hydraulic response or power derate mode activation to protect engine components

Potential Causes

The most common technical causes for Code 335 on used SH350HD-5 excavators include:

• Open circuit in the ECT sensor wiring harness, often caused by wire chafing near the engine block mounting points
• Failed coolant temperature sensor due to internal element deterioration (common after 8,000+ operating hours)
• Corroded or loose connector pins at the sensor plug, especially on machines operated in high-moisture environments
• Damaged ECM wiring between the sensor and control module, particularly at harness flex points near the engine mounts
• Faulty ECM (rare, but possible in machines with electrical system damage history)

How to Troubleshoot and Fix Code 335

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, bent pins, moisture intrusion, or physical damage. On used excavators, check the wiring harness for abrasion points where it contacts the engine or frame—this is a common failure point on the SH350HD-5 model.

Step 2: Electrical Testing Disconnect the ECT sensor connector. Using a digital multimeter, 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). If the reading shows infinite resistance (open circuit) or zero ohms (short circuit), replace the sensor.

Step 3: Harness Continuity Check With the sensor disconnected, check voltage supply at the harness connector. You should measure approximately 5 volts reference voltage from the ECM. Next, test continuity between the sensor connector and ECM pins using wiring diagrams. Any reading above 5 ohms indicates excessive resistance requiring harness repair or replacement.

Step 4: Final Verification After repairs, clear the fault code using diagnostic software (Sumitomo-compatible scan tool or generic OBD interface). Monitor live data during engine warm-up to verify the ECT sensor reads progressive temperature increases from ambient to operating temperature (typically 180-200°F).

Disclaimer: This guide provides general troubleshooting information. Always consult the Sumitomo SH350HD-5 service manual and consider professional diagnostic assistance for complex electrical issues or if you're unfamiliar with high-voltage systems.