What is Hyundai R805LC-7 Fault Code 110-3?

Fault Code 110-3 on the Hyundai R805LC-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 a voltage reading from the coolant temperature sensor circuit that exceeds the manufacturer's specified threshold, typically above 4.8-4.9 volts.

The ECT sensor plays a critical role in the R805LC-7's Cummins QSK23 engine management system by continuously monitoring coolant temperature and relaying this data to the ECM. This information directly influences fuel injection timing, fan engagement, and engine protection protocols. When the ECM receives an abnormally high voltage signal, it interprets this as either an open circuit or sensor malfunction, compromising the engine's ability to regulate operating temperature effectively.

Common Symptoms

• Check Engine Light or malfunction indicator lamp illuminated on the instrument cluster
• Engine may start in derate mode or limp mode, limiting maximum RPM and power output
• Cooling fan runs continuously at high speed, regardless of actual coolant temperature
• Difficulty starting when the engine is cold, as the ECM cannot accurately determine warm-up requirements
• Possible white or black smoke from the exhaust due to incorrect fuel mapping based on faulty temperature readings

Potential Causes

The most common technical causes for Code 110-3 on used R805LC-7 excavators include:

• Open circuit in the coolant temperature sensor wiring harness, often caused by wire chafing near the engine block mounting points
• Failed ECT sensor with internal open circuit (common in machines with 8,000+ operating hours)
• Corroded or loose connector at the sensor terminals or ECM connection points
• Damaged sensor ground circuit, particularly where the harness routes along the valve cover
• ECM internal fault (rare, but possible in high-hour machines experiencing voltage fluctuations)

How to Troubleshoot and Fix Code 110-3

Step 1: Visual Inspection Begin by inspecting the ECT sensor located on the engine block near the thermostat housing. Check for physical damage, coolant leaks around the sensor base, and examine the wiring harness for signs of abrasion, particularly where it contacts the engine or frame. On used excavators, pay special attention to connector corrosion — disconnect and inspect both the sensor connector and the ECM harness connector for green oxidation or bent pins.

Step 2: Electrical Testing Using a digital multimeter, perform a resistance test on the ECT sensor. With the sensor disconnected and at room temperature (approximately 68°F/20°C), you should measure between 2,000-3,000 ohms across the sensor terminals. If the reading shows infinite resistance (OL), the sensor has an internal open circuit and requires replacement. Also check the sensor supply voltage at the harness connector with the ignition on — you should see approximately 5 volts.

Step 3: Wiring Harness Continuity Check Test continuity between the ECM connector and the sensor harness connector for both the signal wire and ground circuit. Any open circuit indicates damaged wiring. For used machines, inspect harness routing for friction points against engine components that may have worn through insulation over thousands of operating hours.

Step 4: Component Replacement and Verification Replace faulty components (typically the ECT sensor or damaged harness sections) using OEM or quality aftermarket parts. After installation, clear the fault code using Hyundai Hi-MATE diagnostic software or an appropriate J1939-compatible scan tool, then monitor for code recurrence during a full heat cycle.

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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 seek assistance from qualified diesel technicians for complex electrical diagnostics or if you're unfamiliar with high-voltage systems.