Sumitomo SH260LC-6 Fault Code 606: Complete Diagnostic Guide

What is Sumitomo SH260LC-6 Fault Code 606?

Fault Code 606 on the Sumitomo SH260LC-6 excavator indicates a malfunction in the engine coolant temperature sensor circuit or an out-of-range coolant temperature reading. This diagnostic trouble code (DTC) is triggered when the Engine Control Module (ECM) detects an abnormal voltage signal from the coolant temperature sensor, typically indicating either a short circuit, open circuit, or sensor failure.

The coolant temperature sensor is critical for this machine's performance because it directly influences fuel injection timing, engine warm-up protocols, and automatic idle control. When this sensor malfunctions, the ECM cannot accurately regulate engine temperature, potentially leading to inefficient combustion, increased emissions, and possible engine protection mode activation.

Common Symptoms

When Code 606 is active on your SH260LC-6, operators typically experience:

• Check Engine Light or malfunction indicator lamp illuminated on the instrument cluster
• Engine running in cold-start mode continuously, causing rough idle and poor fuel economy
• Cooling fan running constantly at high speed regardless of actual engine temperature
• Difficulty achieving normal operating temperature, or conversely, engine overheating without warning
• Potential engine derate or power reduction in protective mode to prevent thermal damage

Potential Causes

The most common technical causes for Code 606 on used SH260LC-6 excavators include:

• Coolant temperature sensor failure due to age-related degradation or internal element breakdown
• Damaged wiring harness between the sensor and ECM, particularly at harness routing points near the engine block where vibration and heat cause insulation wear
• Corroded or loose electrical connectors at the sensor plug—extremely common in machines exposed to moisture or coolant leaks
• ECM internal fault affecting the sensor input circuit (less common but possible in high-hour machines)
• Coolant contamination causing sensor element coating and inaccurate readings
• Incorrect sensor replacement with non-OEM parts having wrong resistance specifications

How to Troubleshoot and Fix Code 606

Step 1: Visual Inspection Begin by locating the coolant temperature sensor on the engine block (typically near the thermostat housing). Inspect the wiring harness for obvious damage, abrasion points, or evidence of coolant leaks that may have contaminated the connector. On used excavators, check for harness wear where it contacts the engine block or frame—a notorious failure point on this model.

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 at the connector with ignition on—you should see approximately 5 volts reference voltage from the ECM. Any reading significantly outside these parameters indicates sensor or wiring failure.

Step 3: Connector and Circuit Verification Inspect the sensor connector pins for corrosion, bent terminals, or moisture intrusion. Clean with electrical contact cleaner and ensure proper seating. Perform a continuity test on the wiring between the sensor connector and ECM to rule out open circuits. Check for shorts to ground using the ohmmeter function.

Step 4: Component Replacement and Verification If testing confirms sensor failure, replace with an OEM-equivalent coolant temperature sensor rated for your specific engine model. After installation, clear codes using diagnostic software (Sumitomo-compatible scan tool or generic J1939 reader) and monitor live data to verify proper temperature readings during warm-up cycle.

Disclaimer: This guide provides general diagnostic information. Always consult the official Sumitomo service manual for your specific serial number and consider professional diagnosis for complex electrical issues or if you're uncomfortable performing these tests on high-voltage systems.