Sumitomo SH210-5 Fault Code 335: Complete Diagnostic Guide

What is Sumitomo SH210-5 Fault Code 335?

Fault Code 335 on the Sumitomo SH210-5 excavator indicates a malfunction in the engine coolant temperature sensor circuit or an abnormal temperature reading detected by the Engine Control Module (ECM). This code specifically triggers when the ECM receives voltage signals outside the normal operating range from the coolant temperature sensor, typically between 0.5-4.5 volts.

The coolant temperature sensor plays a critical role in the SH210-5's performance management system. It directly influences fuel injection timing, idle speed control, and engine protection protocols. When this sensor fails or provides inaccurate data, the ECM cannot properly regulate engine operations, potentially leading to reduced efficiency, increased emissions, or catastrophic overheating damage in these valuable used machines.

Common Symptoms

When Code 335 is active on your SH210-5, operators typically experience:

• Engine warning light illuminated on the instrument panel, often accompanied by audible alarm
• Hard starting or rough idle, particularly when the engine is cold
• Black smoke from exhaust due to improper fuel mixture calculations
• Engine derate mode activation, limiting maximum RPM and hydraulic performance
• Cooling fan running continuously at high speed, even when coolant temperature appears normal

Potential Causes

The most common technical reasons for Code 335 on used SH210-5 excavators include:

• Faulty coolant temperature sensor – internal resistance drift is common after 5,000+ operating hours
• Damaged or corroded wiring harness at connector pins, especially near the engine block where vibration and heat cause insulation breakdown
• Shorted or open circuit in the sensor wiring, particularly at known rub points behind the fuel filter assembly
• Corroded ECM connector terminals (C-series connectors are vulnerable on older units)
• Low coolant level causing intermittent sensor exposure and erratic readings
• Failed ECM (rare, but possible in high-hour machines with electrical system history)

How to Troubleshoot and Fix Code 335

Step 1: Visual Inspection Begin by checking actual coolant level and condition. Inspect the coolant temperature sensor (located on the thermostat housing) and its connector for physical damage, corrosion, or oil contamination. On used excavators, examine the entire harness from sensor to ECM for abrasion points, especially where it passes near moving components.

Step 2: Electrical Testing Using a digital multimeter, disconnect the sensor and measure resistance. At 68°F (20°C), resistance should read approximately 2,000-3,000 ohms (consult your service manual for exact specifications). Check harness continuity and verify supply voltage at the sensor connector is 5.0V ±0.5V with ignition on.

Step 3: Connector and Harness Verification Inspect ECM connectors for "green corrosion" – a common issue in humid environments. Apply dielectric grease after cleaning. Check for voltage drop across connectors under load, which indicates internal terminal corrosion even when visually acceptable.

Step 4: Component Replacement If sensor resistance is out of specification, replace the coolant temperature sensor using OEM or quality aftermarket parts. Clear codes with diagnostic software and verify proper operation through a complete heat cycle.

Disclaimer: This guide provides general diagnostic information. Always consult the official Sumitomo service manual for your specific serial number. Complex electrical diagnostics should be performed by certified technicians with proper diagnostic tools to avoid costly misdiagnosis on used equipment.