Sumitomo SH130-6 Fault Code 1606: Complete Diagnostic Guide

What is Sumitomo SH130-6 Fault Code 1606?

Fault Code 1606 on the Sumitomo SH130-6 excavator indicates a malfunction in the engine coolant temperature (ECT) sensor circuit, specifically detecting an abnormally high voltage signal or open circuit condition. This diagnostic trouble code (DTC) is generated when the Engine Control Module (ECM) receives a voltage reading outside the acceptable range from the coolant temperature sensor, typically above 4.5 volts when normal operating range should be 0.5-4.0 volts.

The ECT sensor plays a critical role in the SH130-6's engine management system by providing real-time temperature data that influences fuel injection timing, idle speed control, and cooling fan operation. When this sensor circuit fails, the ECM cannot properly regulate engine performance, potentially leading to inefficient combustion, increased emissions, and possible engine damage from overheating conditions.

Common Symptoms

When Code 1606 is active on your Sumitomo SH130-6, you may experience:

• Check engine light or malfunction indicator lamp illuminated on the instrument cluster
• Cooling fan running continuously at high speed, even when engine is cold
• Hard starting conditions, especially during cold weather operation
• Rough idle or erratic engine RPM fluctuations during warm-up
• Reduced engine power or derate mode activation to prevent potential overheating damage

Potential Causes

The most common technical reasons for Code 1606 on used SH130-6 excavators include:

• Open circuit in the ECT sensor wiring harness, often caused by wire chafing against the engine block or frame rails near the thermostat housing
• Failed coolant temperature sensor with internal resistance breakdown (common after 5,000+ operating hours)
• Corroded or loose connector pins at the ECT sensor plug, especially on machines exposed to harsh environments
• Damaged ECM wiring at the harness entry point where vibration causes wire fatigue
• ECM internal failure (rare, but possible on high-hour machines with electrical system issues)

How to Troubleshoot and Fix Code 1606

Step 1: Visual Inspection Begin by locating the ECT sensor near the thermostat housing on the engine block. Inspect the sensor connector for corrosion, bent pins, or moisture intrusion. On used excavators, check the entire wiring harness from sensor to ECM for signs of rubbing, cuts, or heat damage. Pay special attention to areas where the harness passes near hot exhaust components or sharp metal edges.

Step 2: Electrical Testing Disconnect the ECT sensor connector and use a digital multimeter to measure resistance across the sensor terminals. At room temperature (68°F/20°C), resistance should read approximately 2,000-3,000 ohms. If reading shows infinite resistance (open circuit) or zero ohms (short circuit), replace the sensor. Next, check for supply voltage at the harness connector with ignition on—you should see approximately 5 volts reference voltage from the ECM.

Step 3: Harness Continuity Check With the sensor disconnected and ignition off, test continuity between the sensor harness connector and ECM pins using wiring diagrams specific to the SH130-6. Check for shorts to ground by measuring resistance between each wire and chassis ground (should read infinite resistance). For used machines, gently wiggle the harness while testing to identify intermittent connection failures caused by internal wire breaks.

Step 4: Final Verification After repairs, clear the fault code using Sumitomo diagnostic software or a compatible scan tool. Run the engine through a complete warm-up cycle while monitoring live ECT sensor data. The temperature reading should gradually rise from ambient to operating temperature (180-200°F) smoothly without sudden jumps or dropouts.

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Disclaimer: This guide provides general diagnostic information for Code 1606. Always consult the official Sumitomo service manual for your specific machine serial number and consider professional diagnosis for complex electrical issues or if you're uncomfortable working with engine management systems.