What is Hyundai Excavator Fault Code 105-2?

Fault Code 105-2 indicates an abnormal voltage signal from the Engine Coolant Temperature (ECT) Sensor Circuit, specifically detecting a voltage reading that is too high (open circuit or sensor failure). This Diagnostic Trouble Code (DTC) is triggered when the Engine Control Module (ECM) receives a signal above the manufacturer's specified voltage threshold, typically above 4.5-4.8 volts, suggesting the sensor circuit is open or the sensor itself has failed.

This code is critical for Hyundai excavators because the ECT sensor directly influences fuel injection timing, engine warm-up cycles, and cooling fan operation. When the ECM cannot accurately read coolant temperature, the engine may run inefficiently, experience hard starts in cold conditions, or enter derate mode to prevent potential overheating damage.

Common Symptoms

• Check Engine Light (CEL) or Malfunction Indicator Lamp (MIL) illuminated on the instrument cluster
• Engine runs excessively rich or fails to reach optimal operating temperature
• Cooling fan runs continuously, even when engine is cold
• Reduced engine power or derate mode activation to protect the engine
• Difficulty starting in cold weather conditions due to improper fuel mapping

Potential Causes

The most common technical reasons for Code 105-2 in used Hyundai excavators include:

• Failed ECT sensor due to internal resistance breakdown (common after 5,000+ operating hours)
• Open circuit in wiring harness between the sensor and ECM, often caused by harness rubbing against engine components near the thermostat housing
• Corroded or loose connector pins at the ECT sensor or ECM connection points
• Damaged sensor ground wire or poor chassis ground connection
• ECM internal fault (rare, but possible in high-hour machines with electrical system stress)

How to Troubleshoot and Fix Code 105-2

Step 1: Visual Inspection Begin by inspecting the ECT sensor located near the thermostat housing. Check for physical damage, coolant leaks, or corrosion on the two-wire connector. On used excavators, verify the wiring harness for friction wear points where it contacts the engine block or brackets.

Step 2: Electrical Testing Disconnect the ECT sensor connector. Using a digital multimeter (DMM), measure resistance across the sensor terminals. At room temperature (68°F/20°C), resistance should read approximately 2,000-3,000 ohms (consult your service manual for exact specifications). If the reading shows infinite resistance (open circuit), replace the sensor.

Step 3: Circuit Verification With the sensor disconnected, measure voltage at the harness connector (ECM side) with ignition ON, engine OFF. You should see approximately 5 volts on the signal wire. If voltage is absent or incorrect, inspect the harness for breaks or shorts, paying special attention to connector terminals for corrosion or bent pins.

Step 4: Ground Circuit Check Verify continuity between the sensor ground wire and chassis ground. Resistance should be less than 1 ohm. High resistance indicates a poor ground connection requiring cleaning or repair.

Step 5: Component Replacement Replace the ECT sensor with a genuine Hyundai OEM part or quality aftermarket equivalent. Clear the fault code using diagnostic software (Hi-SCANPro or equivalent) and monitor for code recurrence after a complete heat cycle.

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Disclaimer: This guide provides general troubleshooting information. Always consult your Hyundai service manual and consider professional diagnostic assistance for complex electrical issues, especially on used equipment with unknown maintenance history.