Sumitomo SH210-6 Fault Code 335: Complete Diagnostic Guide

What is Sumitomo SH210-6 Fault Code 335?

Fault Code 335 on the Sumitomo SH210-6 excavator indicates a malfunction in the engine coolant temperature sensor circuit, specifically detecting an abnormal high voltage signal or open circuit condition in the ECM (Engine Control Module) input.

This code triggers when the coolant temperature sensor sends voltage readings outside the normal operating range (typically above 4.5 volts), suggesting either a disconnected sensor, damaged wiring harness, or complete sensor failure. The engine coolant temperature is critical for the SH210-6's Isuzu engine management system because it directly affects fuel injection timing, throttle response, and automatic warm-up procedures. Ignoring this fault can lead to poor fuel economy, increased emissions, and potential engine damage from improper fuel mixture calculations.

Common Symptoms

When Code 335 is active on your Sumitomo SH210-6, operators typically experience:

• Check Engine Light illuminated on the instrument panel, often accompanied by a diagnostic trouble code warning
• Hard starting or extended cranking time, especially in cold weather conditions when the ECM cannot properly adjust warm-up fuel enrichment
• Rough idle or hunting RPM during the first 10-15 minutes of operation
• Reduced engine power or hesitation during initial acceleration from cold starts
• Cooling fan running continuously at high speed, regardless of actual engine temperature

Potential Causes

The most common technical failures triggering Code 335 on used SH210-6 excavators include:

• Coolant temperature sensor failure due to age-related internal resistance breakdown (common after 5,000+ operating hours)
• Corroded or loose connector pins at the sensor plug, particularly on machines operated in coastal or high-humidity environments
• Wiring harness damage near the thermostat housing where vibration causes insulation wear and potential shorts to ground
• ECM internal circuit degradation affecting the 5-volt reference voltage supply (rare but documented on high-hour machines)
• Aftermarket sensor incompatibility if previous repairs used non-OEM replacement parts with incorrect resistance curves

How to Troubleshoot and Fix Code 335

Step 1: Visual Inspection and Connector Check Locate the coolant temperature sensor on the thermostat housing (driver's side of the Isuzu engine block). Disconnect the two-wire connector and inspect for green corrosion, bent pins, or moisture intrusion. Clean contacts with electrical contact cleaner and verify the rubber seal is intact.

Step 2: Sensor Resistance Testing Using a digital multimeter, measure resistance across the sensor terminals with the engine cold. At 68°F (20°C), resistance should read approximately 2,000-3,000 ohms. Compare readings to the Isuzu specifications chart. If readings show infinite resistance (open circuit) or less than 100 ohms, replace the sensor.

Step 3: Wiring Harness Verification With the sensor disconnected, check continuity between the ECM connector (pins typically labeled THW and E2) and the sensor harness connector. Resistance should be less than 1 ohm. Also verify there's no continuity between either wire and chassis ground, which would indicate a short circuit.

Step 4: ECM Reference Voltage Test Turn the ignition to ON (engine off). Backprobe the sensor connector and measure voltage between the signal wire and ground. You should see approximately 5 volts DC. If voltage is absent or significantly lower, suspect ECM issues or power supply problems.

For used excavators, pay special attention to harness routing near the exhaust manifold where heat degradation commonly occurs on the SH210-6. Check for previous repair attempts using electrical tape rather than proper heat-shrink connectors.

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Disclaimer: This guide provides general diagnostic procedures for Code 335. Always consult the official Sumitomo service manual for your specific machine's serial number range. If you're unfamiliar with electrical diagnostics or lack proper testing equipment, contact a certified Sumitomo/Isuzu technician to avoid misdiagnosis and unnecessary parts replacement.