What is Sumitomo SH290-5 Fault Code 601?

Fault Code 601 on the Sumitomo SH290-5 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 relates to the coolant temperature sensor (also called the water temperature sensor) that monitors engine operating temperature and sends voltage signals to the ECM for proper fuel injection timing, idle speed control, and overheat protection.

This fault is critical for the SH290-5 because the ECM relies on accurate coolant temperature data to optimize engine performance and prevent catastrophic overheating. When Code 601 triggers, the ECM may enter a derate mode or use default temperature values, which can reduce power output and fuel efficiency. For used excavators, this code often appears due to sensor degradation, corroded connectors, or wiring damage from years of exposure to heat and vibration.

Common Symptoms

When Fault Code 601 is active on your SH290-5, you may experience:

• Engine warning light illuminated on the instrument panel
• Hard starting or extended cranking time, especially in cold conditions
• Rough idle or irregular engine RPM fluctuations
• Poor fuel economy due to incorrect fuel mapping
• Engine derate or reduced power output as a protective measure
• Cooling fan running continuously at high speed regardless of actual temperature

Potential Causes

The most common technical reasons for Code 601 on used Sumitomo SH290-5 excavators include:

• Faulty coolant temperature sensor due to internal element failure or contamination from degraded coolant
• Corroded or loose electrical connectors at the sensor or ECM harness connection points
• Damaged wiring harness caused by rubbing against engine components, particularly near the thermostat housing where the sensor typically mounts
• Contaminated coolant causing sensor element fouling or inaccurate readings
• ECM internal fault (less common) affecting the temperature input circuit
• Open or short circuit in the sensor wiring due to age-related insulation breakdown

How to Troubleshoot and Fix Code 601

Step 1: Visual Inspection Begin by locating the coolant temperature sensor on the engine block (typically near the thermostat housing). Inspect the sensor connector for corrosion, oil contamination, or loose pins. Check the wiring harness for obvious damage, melted insulation, or wear points where it contacts engine components. On used excavators, pay special attention to connector seals that may have hardened over time.

Step 2: Electrical Testing Using a digital multimeter, disconnect the sensor and measure its resistance. 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 harness voltage with the key on, engine off—you should see approximately 5 volts at the connector from the ECM. Check for continuity between the sensor ground and chassis ground.

Step 3: Sensor and Harness Evaluation If resistance readings are out of specification or the sensor shows no change when heated, replace the coolant temperature sensor. Before installation, clean the mounting threads and apply fresh thread sealant. If harness voltage is absent or incorrect, trace wiring back to the ECM, checking for shorts to ground or open circuits. For used machines, consider replacing the entire sensor pigtail if corrosion is present. After repairs, clear the code using diagnostic software (Sumitomo SWS or compatible tool) and monitor for recurrence during a full heat cycle.

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Disclaimer: This guide provides general troubleshooting information for Sumitomo SH290-5 Fault Code 601. Always consult the manufacturer's service manual and consider professional diagnostic assistance for complex electrical issues or if you lack proper testing equipment. Improper repairs can cause further damage to ECM components.