What is Hyundai Excavator Fault Code 150-6?

Fault Code 150-6 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 triggered when the Engine Control Module (ECM) receives a voltage reading from the coolant temperature sensor that exceeds the normal operating range (typically above 4.5-4.8 volts), suggesting either a disconnected sensor, damaged wiring harness, or sensor internal failure.

This code is critical for Hyundai excavators because the ECT sensor provides essential data for fuel injection timing, engine warm-up enrichment, and cooling fan activation. When the ECM cannot accurately monitor engine temperature, it may default to a fail-safe mode that limits machine performance and can lead to potential engine damage from overheating or inefficient combustion.

Common Symptoms

• Check Engine Light or warning indicator illuminated on the instrument cluster
• Engine runs in cold-start mode continuously, causing rough idle and black smoke from excessive fuel enrichment
• Reduced engine power or derate mode activated as a protective measure
• Cooling fan runs constantly at maximum speed regardless of actual engine temperature
• Difficulty starting when the engine is warm, or prolonged cranking during cold starts

Potential Causes

The most frequent causes of Code 150-6 on used Hyundai excavators include:

• Open circuit in the ECT sensor wiring harness, often caused by wire breakage near flex points or engine mounting brackets
• Corroded or loose connector pins at the ECT sensor connection—common in machines exposed to harsh environments or improper washing procedures
• Failed ECT sensor with internal open circuit, particularly in older excavators with 5,000+ operating hours
• Damaged wiring insulation due to rubbing against engine components, exhaust manifolds, or vibration-induced wear
• ECM internal fault (rare) affecting the sensor reference voltage circuit

How to Troubleshoot and Fix Code 150-6

Step 1: Visual Inspection Begin by locating the ECT sensor (typically installed in the engine coolant passage near the thermostat housing). Inspect the wiring harness from sensor to ECM for visible damage, chafing, or burns. On used excavators, pay special attention to areas where harnesses pass near hot exhaust components or moving parts.

Step 2: Connector and Sensor Testing Disconnect the ECT sensor connector and inspect for corrosion, moisture, or bent pins. Using a digital multimeter, measure the resistance across the sensor terminals with the engine cold (should read approximately 2,000-3,000 ohms at 68°F/20°C). Compare readings to manufacturer specifications in your service manual.

Step 3: Circuit Voltage Check With the sensor disconnected and ignition ON, measure voltage at the ECM harness side of the 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 for breaks or shorts.

Step 4: Repair or Replace If sensor resistance is out of specification, replace the ECT sensor with a genuine Hyundai or OEM-equivalent part. If wiring damage is found, repair using proper gauge wire and heat-shrink connections—avoid electrical tape on used machinery where vibration can cause failures. Clear the fault code using Hyundai diagnostic software (Hi-TMAP or compatible scan tool) and verify repair by monitoring live coolant temperature data during operation.

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