What is Hyundai R455LC-7 Fault Code 718-11?

Fault Code 718-11 on the Hyundai R455LC-7 excavator indicates a Hydraulic Oil Temperature Sensor Circuit Low Voltage condition. This diagnostic trouble code (DTC) is triggered when the Electronic Control Module (ECM) detects an abnormally low voltage signal from the hydraulic oil temperature sensor, typically below 0.5 volts. The sensor monitors the temperature of the hydraulic oil in the main system, and accurate readings are critical for the ECM to prevent overheating, optimize hydraulic performance, and protect expensive pump and motor assemblies on this 45-ton class excavator.

In the R455LC-7's hydraulic system, proper oil temperature management directly affects system efficiency, component longevity, and operational safety. When this code activates, the ECM may default to conservative operating parameters to prevent potential damage.

Common Symptoms

When fault code 718-11 is active, operators typically experience:

• Warning light illuminated on the instrument cluster, often accompanied by a hydraulic system alert
• Reduced hydraulic performance or derated machine functions as the ECM enters protective mode
• Inaccurate temperature gauge readings showing extremely low or erratic hydraulic oil temperatures
• Intermittent loss of power during operation, particularly in high-demand digging or lifting tasks
• Error messages displayed on the monitor panel indicating hydraulic system faults

Potential Causes

Several technical issues commonly trigger this fault code on used R455LC-7 excavators:

• Damaged or shorted wiring harness between the temperature sensor and ECM, particularly at routing points near the hydraulic tank where vibration and heat cycling cause insulation breakdown
• Corroded or loose electrical connectors at the sensor plug, allowing moisture intrusion (common in machines with 3,000+ operating hours)
• Failed hydraulic oil temperature sensor, showing internal short-circuit or ground fault
• ECM internal circuit failure affecting the sensor signal processing circuit
• Chafed wiring at known rub points along the main frame, especially where harnesses pass near rotating components or sharp edges
• Poor ground connections in the chassis grounding system affecting sensor reference voltage

How to Troubleshoot and Fix Code 718-11

Step 1: Visual Inspection Begin with a thorough physical inspection of the hydraulic oil temperature sensor located on the hydraulic oil tank. Check the sensor connector for corrosion, bent pins, or oil contamination. On used excavators, pay special attention to the wiring harness routing from the sensor to the ECM—look for abraded insulation, especially where the harness contacts the frame or passes through bulkheads.

Step 2: Electrical Testing Using a digital multimeter (DMM), disconnect the sensor and measure resistance across the sensor terminals. A functional sensor typically reads 2,000-3,000 ohms at room temperature (consult the R455LC-7 service manual for exact specifications). Next, check for continuity between each sensor wire and ground with the harness connected—any continuity indicates a short to ground. Measure supply voltage at the sensor connector with ignition on; it should read approximately 5 volts.

Step 3: Advanced Diagnostics Connect Hyundai Hi-MATE diagnostic software or compatible scan tool to retrieve freeze frame data and observe live sensor voltage. A reading consistently below 0.3 volts confirms the low voltage condition. Inspect the ECM connector pins (C106 harness connector) for corrosion or terminal push-back. On high-hour used machines, consider checking the chassis ground strap between the engine and frame for corrosion resistance.

Step 4: Component Replacement If testing confirms sensor failure, replace the hydraulic oil temperature sensor (Hyundai part number varies by production year). When installing, apply dielectric grease to connector terminals to prevent future corrosion. If wiring damage is found, repair using sealed heat-shrink connectors and reroute away from heat sources and pinch points. After repairs, clear the fault code and perform a hydraulic system warm-up cycle to verify proper sensor operation across the temperature range.

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Disclaimer: This guide provides general troubleshooting information for fault code 718-11. Always consult the official Hyundai R455LC-7 service manual and schematic diagrams for your specific machine's serial number. If you're unfamiliar with electrical diagnostics or hydraulic systems, consult a certified Hyundai heavy equipment technician to prevent injury or further damage to the excavator.