Sumitomo SH240-6 Fault Code 606: Complete Diagnostic Guide

What is Sumitomo SH240-6 Fault Code 606?

Fault Code 606 on the Sumitomo SH240-6 excavator indicates a malfunction in the engine coolant temperature sensor circuit or an abnormal coolant temperature reading detected by the ECM (Engine Control Module). This code triggers when the control system receives signals outside the normal operating range, typically between 0.5-4.5 volts from the coolant temperature sensor.

This diagnostic trouble code is critical because the ECM relies on accurate coolant temperature data to optimize fuel injection timing, manage engine protection protocols, and control hydraulic oil temperature. On used excavators like the SH240-6, this sensor failure can lead to improper engine management, reduced fuel efficiency, and potential overheating damage to expensive engine components.

Common Symptoms

When Code 606 is active on your Sumitomo SH240-6, you may experience:

• Engine warning light illuminated on the operator display panel
• Hard starting conditions, especially during cold weather operation
• Excessive black smoke from the exhaust due to improper fuel mixture
• Engine derate mode where power output is automatically limited to prevent damage
• Erratic temperature gauge readings or gauge stuck at minimum/maximum positions
• Cooling fan running continuously regardless of actual engine temperature

Potential Causes

The most common technical causes for Code 606 on used SH240-6 excavators include:

• Faulty coolant temperature sensor (resistance out of specification, typically should be 2,000-3,000 ohms at 68°F)
• Damaged wiring harness near the engine block where heat and vibration cause insulation breakdown
• Corroded or loose connector pins at the sensor or ECM connection points
• Shorted or open circuit in the sensor signal wire (common at harness routing points near the exhaust manifold)
• Failed ECM (rare, but possible on high-hour used machines)
• Coolant contamination causing sensor element fouling or corrosion

How to Troubleshoot and Fix Code 606

Step 1: Visual Inspection Begin by inspecting the coolant temperature sensor located on the engine block near the thermostat housing. Check for physical damage, coolant leaks, or corrosion on the connector. On used excavators, examine the wiring harness for rubbing points, heat damage, or rodent damage along the entire length from sensor to ECM.

Step 2: Electrical Testing Using a digital multimeter, disconnect the sensor and measure resistance across the sensor terminals. Compare readings to the manufacturer's specification chart (resistance decreases as temperature increases). Check for continuity in the signal wire and verify proper ground connection with less than 1 ohm resistance.

Step 3: Circuit Voltage Check With the ignition on and sensor disconnected, measure voltage at the harness connector. You should see approximately 5 volts reference voltage from the ECM. If voltage is absent or incorrect, trace the wiring back to the ECM, checking for shorts to ground or open circuits.

Step 4: Component Replacement If the sensor tests faulty, replace it with a genuine Sumitomo or OEM-equivalent part, applying anti-seize compound to threads. For used excavators with high hours, consider replacing the connector pigtail simultaneously, as corrosion often affects both components. Clear codes using diagnostic software and verify repair with a test cycle.

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Disclaimer: This guide provides general diagnostic information for the Sumitomo SH240-6. Always consult the manufacturer's service manual and consider professional diagnostic services for complex electrical issues or if you're unfamiliar with high-voltage systems.