Sumitomo SH350HD-5 Fault Code 336: Complete Diagnostic Guide

What is Sumitomo SH350HD-5 Fault Code 336?

Fault Code 336 on the Sumitomo SH350HD-5 excavator indicates a malfunction in the Engine Coolant Temperature (ECT) sensor circuit or an abnormal coolant temperature reading detected by the Engine Control Module (ECM). This code specifically signals that the ECM has detected a voltage signal outside the acceptable range from the coolant temperature sensor, typically caused by sensor failure, wiring issues, or actual overheating conditions.

The ECT sensor plays a critical role in the SH350HD-5's engine management system by providing real-time temperature data that controls fuel injection timing, idle speed, and cooling fan operation. When this sensor circuit malfunctions, the ECM defaults to failsafe mode, which can significantly impact machine performance and fuel efficiency. For used excavators, this code often indicates age-related sensor degradation or harness damage from years of vibration and heat cycles.

Common Symptoms

When Code 336 is active on your SH350HD-5, operators typically experience:

• Check Engine light illuminated on the instrument cluster with possible warning buzzer activation
• Hard starting or rough idling, especially during cold starts when the ECM relies heavily on temperature data
• Cooling fan running continuously at high speed, even when engine temperature appears normal
• Reduced engine power or derate mode activation as the ECM limits performance to prevent potential overheating damage
• Erratic temperature gauge readings or gauge stuck in one position despite actual temperature changes

Potential Causes

The most common technical causes for Code 336 on used SH350HD-5 excavators include:

• Failed coolant temperature sensor due to internal resistance drift or element corrosion (very common on machines with 5,000+ hours)
• Damaged sensor wiring harness near the engine block where vibration causes wire chafing against metal surfaces
• Corroded or loose electrical connectors at the sensor or ECM connection points, especially after exposure to coolant leaks
• Actual engine overheating condition triggering legitimate high-temperature warnings
• ECM internal fault or corrupted calibration data (rare, but possible on older control modules)
• Faulty thermostat causing genuine temperature regulation problems that trigger sensor circuit diagnostics

How to Troubleshoot and Fix Code 336

Step 1: Visual Inspection and Code Verification

Connect a diagnostic laptop with Sumitomo-compatible software or a universal heavy equipment scanner to confirm Code 336 and check for additional codes. Perform a thorough visual inspection of the ECT sensor (located on the engine block near the thermostat housing) and trace the wiring harness back to the ECM. Look specifically for coolant residue, cracked insulation, or connectors with green corrosion—common issues on used machines.

Step 2: Electrical Testing

Disconnect the coolant temperature sensor connector and measure resistance across the sensor terminals using a digital multimeter. At room temperature (68°F/20°C), resistance should typically read between 2,000-3,000 ohms (consult your service manual for exact specifications). Test the wiring harness for continuity between the sensor connector and ECM pins, and check for shorts to ground. Measure supply voltage from the ECM (typically 5V reference) with the ignition on.

Step 3: Component Replacement and Verification

If sensor resistance is out of specification or wiring shows damage, replace the faulty component. For used excavators, always inspect connector terminals for wear and apply dielectric grease to prevent future corrosion. After repairs, clear the fault code, run the engine through full temperature cycles, and monitor with diagnostic software to ensure the code doesn't return.

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Disclaimer: This guide provides general troubleshooting information for the Sumitomo SH350HD-5. Always consult the manufacturer's service manual and consider professional diagnostic assistance for complex electrical issues or if you're unfamiliar with high-voltage systems.