What is Case CX220C Fault Code 606?

Fault Code 606 on the Case CX220C excavator indicates a malfunction in the Engine Coolant Temperature (ECT) Sensor Circuit, specifically detecting a voltage reading that is too high or an open circuit condition. This diagnostic trouble code (DTC) is generated by the Electronic Control Module (ECM) when it receives an abnormally high voltage signal (typically above 4.8 volts) from the coolant temperature sensor or detects no signal at all.

The ECT sensor plays a critical role in the Case CX220C's engine management system by providing real-time coolant temperature data to the ECM. This information directly affects fuel injection timing, idle speed control, and engine protection protocols. When Code 606 is active, the ECM switches to default temperature values, which can compromise engine efficiency and potentially lead to overheating or poor cold-start performance on used machines with accumulated wear.

Common Symptoms

• Check Engine Light or warning lamp illuminated on the instrument cluster
• Hard starting conditions, especially during cold weather operation
• Rough idle or unstable engine RPM when the machine first starts
• Increased fuel consumption due to ECM operating in failsafe mode with default temperature parameters
• Engine derate or power loss in severe cases where the ECM limits performance to protect components

Potential Causes

The most common causes of Code 606 on used Case CX220C excavators include:

• Open circuit in the ECT sensor wiring harness, often caused by wire breakage or connector damage from vibration
• Failed Engine Coolant Temperature sensor with internal resistance breakdown (common after 5,000+ operating hours)
• Corroded or loose connector pins at the sensor or ECM connection points—especially prevalent in machines exposed to harsh environments
• Chafed wiring where the harness contacts the engine block or frame rails (known wear point on CX220C models)
• ECM internal fault (rare, but possible in high-hour used machines)

How to Troubleshoot and Fix Code 606

Step 1: Visual Inspection Begin by inspecting the ECT sensor connector located near the thermostat housing on the engine block. Check for corrosion, bent pins, moisture intrusion, or physical damage. On used excavators, carefully trace the sensor harness looking for rubbed-through insulation where it passes near hot or moving components.

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. Compare readings to Case specifications. Also check for continuity between sensor ground and chassis ground.

Step 3: Circuit Voltage Check With the sensor disconnected and ignition ON (engine OFF), measure voltage at the harness connector. You should see approximately 5 volts on the signal wire. If voltage reads near battery voltage (12V) or zero, the problem lies in the wiring harness or ECM.

Step 4: Repair or Replace Replace the ECT sensor if resistance readings are out of specification. If the sensor tests good, repair damaged wiring or clean corroded connectors. For used machines, apply dielectric grease to connector pins to prevent future corrosion. Clear the code using Case diagnostic software (ServiceMaster or equivalent) and verify repair with a test run.

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Disclaimer: This guide provides general troubleshooting information. Always consult the Case CX220C service manual and consider professional diagnostic assistance for complex electrical issues or if you lack proper diagnostic equipment.