Sumitomo SH240-6 Fault Code 335: Complete Diagnostic Guide

What is Sumitomo SH240-6 Fault Code 335?

Fault Code 335 on the Sumitomo SH240-6 excavator indicates a malfunction in the Engine Coolant Temperature (ECT) sensor circuit, specifically reporting an abnormal voltage signal or out-of-range temperature reading to the Engine Control Module (ECM).

This diagnostic trouble code triggers when the ECM detects voltage readings outside the normal operating range (typically 0.5-4.5 volts) from the coolant temperature sensor. The ECT sensor is critical for proper fuel injection timing, engine warm-up cycles, and preventing overheating conditions on the Isuzu engine powering the SH240-6. When this code activates, the ECM may default to a predetermined temperature value, which can affect engine performance, fuel efficiency, and emission control systems.

Common Symptoms

When Code 335 is active on your SH240-6, operators typically experience:

• Check Engine Light illuminated on the instrument panel with possible engine derate mode
• Hard starting conditions, especially during cold weather operation
• Rough idle or irregular engine RPM fluctuations during warm-up
• Poor fuel economy and black smoke from the exhaust stack
• Engine overheating warnings even when coolant temperature appears normal

Potential Causes

The most common technical failures triggering Code 335 on used SH240-6 excavators include:

• Faulty ECT sensor with internal resistance drift (common after 5,000+ operating hours)
• Corroded or damaged wiring harness connections at the sensor plug, particularly where the harness passes near the engine block
• Broken or frayed sensor wires due to vibration wear at harness routing points along the valve cover
• Contaminated coolant affecting sensor accuracy or causing sensor element corrosion
• Poor ground connection at the ECM or sensor ground circuit
• 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 near the thermostat housing. Check for coolant leaks, corrosion on the connector pins, and physical damage. On used excavators, carefully examine the wiring harness for rubbing points against metal brackets or heat shields—a common failure point on the SH240-6.

Step 2: Electrical Testing Using a digital multimeter, disconnect the ECT sensor connector and measure resistance across the sensor terminals. At 68°F (20°C), resistance should read approximately 2,000-3,000 ohms. Compare readings against Sumitomo's specification chart. Also check for continuity between the sensor connector and ECM pins, looking for open circuits or excessive resistance (should be less than 5 ohms).

Step 3: Voltage Check With the ignition on and sensor disconnected, check for reference voltage at the harness connector (should read approximately 5 volts). If voltage is absent or incorrect, trace the circuit back to the ECM for potential wiring faults or ECM issues.

Step 4: Sensor Replacement and Verification If testing confirms sensor failure, replace the ECT sensor using OEM or quality aftermarket parts. Apply anti-seize compound to threads and ensure proper torque (typically 15-20 ft-lbs). After replacement, clear codes using diagnostic software and verify the system operates correctly through a complete heat cycle.

Disclaimer: This guide provides general troubleshooting information. Always consult the Sumitomo SH240-6 service manual and consider professional diagnostic assistance for complex electrical issues or if you're unfamiliar with excavator systems.