What is Hyundai R455LC-7 Fault Code 100-18?

Fault Code 100-18 on the Hyundai R455LC-7 excavator indicates an Engine Coolant Temperature (ECT) Sensor Circuit Low Voltage condition. This diagnostic trouble code (DTC) is triggered when the Engine Control Module (ECM) detects a voltage signal from the coolant temperature sensor that falls below the manufacturer's specified threshold, typically under 0.2 volts.

The ECT sensor plays a critical role in the R455LC-7's performance management system by monitoring engine operating temperature and sending real-time data to the ECM. This information directly affects fuel injection timing, idle speed control, and engine protection protocols. On used excavators, this sensor circuit failure can lead to incorrect temperature readings, causing the ECM to make improper fuel delivery decisions that reduce efficiency and potentially damage the engine.

Common Symptoms

When Code 100-18 is active on your Hyundai R455LC-7, you may experience:

• Check Engine Light or malfunction indicator lamp illuminated on the instrument cluster
• Difficult cold starts or extended cranking time, as the ECM assumes incorrect coolant temperature
• Engine derate mode activated, limiting power output to protect against perceived overheating
• Rough idling or irregular engine speed, particularly when the machine is cold
• Cooling fans running continuously at full speed regardless of actual engine temperature

Potential Causes

The most common technical causes for Code 100-18 on used R455LC-7 excavators include:

• Damaged or corroded wiring harness between the ECT sensor and ECM, particularly at known rub points near the engine block mounting brackets
• Failed coolant temperature sensor due to internal short circuit or contamination from degraded coolant
• Broken or corroded connector pins at the sensor plug, common in machines with high operating hours
• ECM internal circuit failure, though less common than sensor or wiring issues
• Low coolant level causing sensor exposure to air rather than coolant (creating erratic readings)
• Damaged sensor ground wire or poor ground connection at the engine block

How to Troubleshoot and Fix Code 100-18

Step 1: Visual Inspection Begin by inspecting the ECT sensor located on the engine block near the thermostat housing. Check the wiring harness for obvious damage, abrasion, or moisture intrusion. On used excavators, pay special attention to areas where the harness contacts metal surfaces or routing clips that may have degraded over time.

Step 2: Electrical Testing Using a digital multimeter, disconnect the ECT sensor connector and measure resistance across the sensor terminals. At room temperature (68°F/20°C), resistance should typically read between 2,000-3,000 ohms. Compare your reading to Hyundai's specification chart. Also check for continuity between the sensor connector and ECM pins to verify wiring integrity.

Step 3: Voltage Check With the ignition on and sensor disconnected, measure reference voltage at the harness connector. You should see approximately 5 volts from the ECM. A reading significantly lower indicates a wiring problem or ECM issue. Check the ground circuit for continuity and resistance below 1 ohm.

Step 4: Component Replacement If electrical tests confirm sensor failure, replace the ECT sensor using a genuine Hyundai or OEM-equivalent part. Before installation, inspect the sensor mounting boss for corrosion and apply anti-seize compound to threads. For used machines, replace the connector terminals if any corrosion is present to prevent recurring codes.

Step 5: System Verification After repairs, clear the fault code using Hyundai Hi-MATE diagnostic software or a compatible scan tool. Run the engine through a complete warm-up cycle while monitoring live ECT data to confirm proper sensor operation and verify the code does not return.

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Disclaimer: This guide provides general troubleshooting information for Code 100-18. Always consult the official Hyundai R455LC-7 service manual and consider seeking assistance from a certified heavy equipment technician for complex electrical diagnostics or if you're unfamiliar with high-voltage systems.