What is Hyundai R455LC-7 Fault Code 111-2?

Fault Code 111-2 on the Hyundai R455LC-7 excavator indicates an Engine Coolant Temperature (ECT) Sensor Circuit High Voltage condition. This diagnostic trouble code (DTC) is triggered when the Engine Control Module (ECM) detects an abnormally high voltage signal from the coolant temperature sensor circuit, typically reading above 4.8-4.9 volts when the expected range is 0.5-4.5 volts.

The ECT sensor plays a critical role in engine management by monitoring coolant temperature and sending real-time data to the ECM. This information controls fuel injection timing, idle speed adjustments, and engine protection protocols. On used excavators like the R455LC-7, this code directly impacts engine efficiency and can trigger protective derate modes to prevent overheating damage to the Cummins QSX15 engine commonly found in this model.

Common Symptoms

When Code 111-2 is active, operators typically experience:

• Check Engine Light illuminated on the instrument cluster with possible engine derate mode activated
• Inaccurate coolant temperature gauge readings, often showing extremely cold temperatures regardless of actual engine condition
• Hard starting when engine is warm, as the ECM incorrectly interprets engine temperature
• Poor fuel economy and black smoke from exhaust due to improper fuel mapping
• Engine running in "limp mode" with reduced power output to protect components

Potential Causes

The most common technical reasons for Code 111-2 on used Hyundai excavators include:

• Open circuit in ECT sensor wiring harness, particularly where the harness routes near the engine block where heat and vibration cause insulation breakdown
• Failed coolant temperature sensor with internal open circuit (common after 5,000+ operating hours)
• Corroded or damaged connector pins at the ECT sensor plug, especially on machines operating in wet or marine environments
• Chafed wiring at known rub points near the fuel filter housing and along the valve cover
• ECM internal fault (rare, but possible on high-hour machines with moisture intrusion)

How to Troubleshoot and Fix Code 111-2

Step 1: Visual Inspection Begin with a thorough inspection of the ECT sensor connector located on the thermostat housing. Disconnect the 2-pin connector and examine for corrosion, bent pins, or moisture. On used excavators, this connector often shows green corrosion due to coolant weeping. Clean with electrical contact cleaner and apply dielectric grease.

Step 2: Sensor Resistance Testing Using a digital multimeter (DMM), measure the resistance across the ECT sensor terminals with the engine cold. You should read approximately 2,000-3,000 ohms at 68°F (20°C). If the reading shows infinite resistance (OL), the sensor has an internal open circuit and requires replacement. The OEM part number is 39B4-11570 for the R455LC-7.

Step 3: Wiring Harness Continuity Check Disconnect the ECM connector (typically a 120-pin connector behind the operator cab). Check continuity between the ECT sensor connector and the ECM pins (refer to wiring diagram for specific pin locations). Also check for short to voltage by measuring voltage with the key on, engine off—it should read 5 volts reference voltage from the ECM. Inspect harness routing for wear points, particularly where it passes through metal grommets.

Step 4: Advanced Diagnostics If sensor and wiring test normal, use Hyundai Hi-MATE or compatible diagnostic software to monitor live ECT sensor data. Compare actual coolant temperature (use infrared thermometer) versus displayed temperature. A significant discrepancy indicates ECM calibration issues or internal ECM failure requiring dealer-level diagnostics.

For used excavators, pay special attention to previous repair attempts—aftermarket sensors or improper wire repairs often cause recurring issues. Always verify connector seals are intact to prevent moisture ingress.

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Disclaimer: This guide provides general troubleshooting information. Always consult the official Hyundai service manual for your specific machine serial number, and consider professional diagnostic assistance for complex electrical issues. Improper repairs can cause additional damage to engine management systems.