Sumitomo SH350HD-6 Fault Code 335: Complete Diagnostic Guide

What is Sumitomo SH350HD-6 Fault Code 335?

Fault Code 335 on the Sumitomo SH350HD-6 indicates a malfunction in the swing motor proportional solenoid valve circuit, specifically detecting an abnormal electrical current or open/short circuit condition in the swing control system. This code is generated when the Electronic Control Module (ECM) detects voltage or current values outside the manufacturer's specified parameters for the swing motor's proportional control valve.

This fault is critical for the SH350HD-6 because the swing system relies on precise solenoid valve operation to control hydraulic flow to the swing motor. Any disruption in the electrical signal can result in erratic swing behavior, reduced operational efficiency, or complete loss of swing function—severely impacting productivity on job sites where 360-degree rotation is essential.

Common Symptoms

When Code 335 is active on your Sumitomo excavator, operators typically experience:

• Intermittent or complete loss of swing function, with the upper structure failing to rotate smoothly or at all
• Erratic swing speed control, where the swing motion becomes unpredictable or jerky during operation
• Warning indicator illumination on the dashboard display panel, often accompanied by an audible alarm
• Reduced swing torque or slow response when initiating swing movements
• Machine entering derate mode, limiting overall hydraulic system performance to protect components

Potential Causes

The most common technical causes for Code 335 on used SH350HD-6 excavators include:

• Damaged or corroded wiring harness connections at the swing motor proportional solenoid valve, particularly at connector points exposed to moisture and debris
• Failed proportional solenoid valve due to internal coil breakdown, contamination, or wear from extended service hours
• Chafed or pinched wiring along the swing post area where the harness rotates with the upper structure—a known wear point on aging machines
• Corroded connector pins at the ECM or valve connector, causing high resistance or intermittent open circuits
• ECM internal fault or software calibration issues (less common but possible on high-hour used equipment)
• Hydraulic contamination causing the solenoid valve spool to stick, increasing electrical current draw

How to Troubleshoot and Fix Code 335

Step 1: Visual Inspection Begin by inspecting the swing motor proportional solenoid valve and its associated wiring harness. Check for obvious damage, oil contamination on connectors, frayed wires, or corrosion on connector pins. On used excavators, pay special attention to the rotating harness section along the swing post—this is a common failure point due to repeated flexing.

Step 2: Electrical Testing Using a digital multimeter, disconnect the solenoid valve connector and measure the coil resistance. Typical specifications for Sumitomo proportional solenoids range from 8-15 ohms (consult your service manual for exact values). Check for short circuits to ground and verify continuity through the entire harness back to the ECM connector. Measure supply voltage at the connector with the ignition on—should read approximately 12-24V depending on system design.

Step 3: Diagnostic Software Analysis Connect Sumitomo-compatible diagnostic software (or universal heavy equipment scanners with Sumitomo protocols) to monitor real-time current draw to the solenoid valve during operation. Compare values against factory specifications. This helps identify intermittent electrical faults that static testing might miss.

Step 4: Component Replacement or Repair If resistance or voltage values are out of specification, replace the proportional solenoid valve or repair damaged harness sections. For used machines, always replace connector pins showing any corrosion and apply dielectric grease to prevent future moisture intrusion. Clear the fault code and perform a function test, cycling the swing operation through full range of motion under varying loads.

Disclaimer: This guide provides general diagnostic information. Always consult the official Sumitomo service manual for your specific serial number and seek qualified professional assistance for complex electrical or hydraulic repairs. Improper diagnosis can lead to equipment damage or safety hazards.