What is Sumitomo SH220LC-6 Fault Code 335?

Fault Code 335 on the Sumitomo SH220LC-6 excavator indicates a malfunction in the engine coolant temperature sensor circuit, specifically detecting an abnormally high voltage signal or open circuit condition. This diagnostic trouble code (DTC) is generated when the Engine Control Module (ECM) receives voltage readings outside the acceptable range from the coolant temperature sensor, typically above 4.5 volts when normal operation should show 0.5-4.0 volts depending on temperature.

This code is critical for the SH220LC-6 because the ECM relies on accurate coolant temperature data to manage fuel injection timing, engine protection protocols, and hydraulic system warm-up cycles. When this sensor circuit fails, the ECM cannot properly protect the engine from overheating conditions or optimize performance based on operating temperature.

Common Symptoms

When Code 335 is active on your Sumitomo SH220LC-6, operators typically experience:

• Engine warning light illuminated on the instrument panel, often accompanied by a diagnostic lamp
• Hard starting conditions, especially during cold weather, as the ECM defaults to a fixed temperature value
• Poor fuel economy and rough idle due to incorrect fuel delivery calculations
• Engine may enter derate mode or limited power output to protect components from potential overheating
• Inaccurate temperature gauge readings showing extremely cold temperatures even when engine is warm

Potential Causes

The most common technical reasons for Code 335 on used SH220LC-6 excavators include:

• Open circuit in sensor wiring harness due to wire breakage, particularly where the harness routes near the engine block and experiences vibration stress
• Corroded or damaged connector pins at the coolant temperature sensor plug, common in machines with high operating hours in wet or corrosive environments
• Failed coolant temperature sensor, where internal resistance becomes infinite (open circuit)
• Chafed wiring at known rub points near the engine mount brackets or against sharp metal edges
• ECM connector corrosion affecting the sensor signal return circuit
• Previous repair attempts using incorrect sensor specifications or aftermarket sensors with incompatible resistance curves

How to Troubleshoot and Fix Code 335

Step 1: Visual Inspection Begin by inspecting the coolant temperature sensor located on the engine block near the thermostat housing. Check the wiring harness for obvious damage, chafing, or corrosion. On used excavators, pay special attention to areas where harnesses contact frame members or experience repetitive movement. Disconnect the sensor connector and inspect pins for corrosion, bent terminals, or moisture intrusion.

Step 2: Sensor and Circuit Testing Using a digital multimeter, measure resistance across the sensor terminals with the sensor disconnected. At room temperature (68°F/20°C), resistance should read approximately 2,000-3,000 ohms (consult service manual for exact specifications). If resistance reads infinite (OL), the sensor has failed internally. Next, check for continuity between each sensor wire and ground; any continuity indicates a short circuit requiring harness repair.

Step 3: Voltage Signal Verification With the sensor connected and ignition on (engine off), backprobe the ECM connector using a multimeter to measure sensor signal voltage. Readings consistently above 4.5 volts confirm an open circuit condition. Check the sensor ground circuit by measuring voltage drop between the sensor ground terminal and battery negative while cranking—readings above 0.1 volts indicate ground circuit problems.

Step 4: Repair or Replace Components For used excavators, replace the coolant temperature sensor only after confirming wiring integrity, as sensor failure and harness damage often occur together. Use OEM-specification sensors to ensure proper resistance curves. Repair any damaged harness sections with high-temperature automotive wire and protect repairs with heat shrink tubing and split loom. Apply dielectric grease to connector pins before reassembly to prevent future corrosion.

Step 5: Clear Code and Verify After repairs, clear the fault code using Sumitomo diagnostic software or by disconnecting the battery for 5 minutes. Run the engine through a complete warm-up cycle while monitoring coolant temperature readings to verify proper sensor operation and confirm the code does not return.

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Disclaimer: This guide provides general troubleshooting information for Sumitomo SH220LC-6 excavators. Always consult the manufacturer's service manual for model-specific procedures and specifications. If you're uncomfortable performing electrical diagnostics, consult a certified heavy equipment technician to prevent further damage to electronic systems.