Hyundai R455LC-7 Fault Code 1351-3: Technical Guide

What is Hyundai R455LC-7 Fault Code 1351-3?

Fault Code 1351-3 indicates an abnormal electrical condition in the engine coolant temperature sensor circuit, specifically a voltage signal that is above the expected range (high voltage/open circuit condition). This code is triggered when the Engine Control Module (ECM) detects a sensor voltage exceeding 4.5-4.8 volts, typically indicating an open circuit, damaged sensor, or wiring fault.

The Hyundai R455LC-7 uses a negative temperature coefficient (NTC) thermistor for coolant temperature monitoring. This sensor is critical because the ECM relies on accurate coolant temperature data to control fuel injection timing, fan operation, and engine protection systems. When this circuit fails, the machine may enter derate mode to prevent potential engine damage from operating without proper temperature monitoring.

Common Symptoms

When Code 1351-3 is active on your R455LC-7, operators typically experience:

• Warning light illuminated on the instrument cluster (check engine or coolant temperature warning)
• Cooling fan running continuously at high speed, regardless of actual engine temperature
• Engine power derate or limited throttle response as a protective measure
• Inaccurate temperature gauge readings showing maximum temperature or erratic fluctuations
• Difficulty starting in cold conditions due to improper fuel enrichment calculations

Potential Causes

The most common causes of Code 1351-3 on used R455LC-7 excavators include:

• Coolant temperature sensor failure – internal sensor element open circuit (common after 5,000+ hours)
• Damaged wiring harness – particularly at flex points near the engine mount where vibration causes wire breakage
• Corroded or loose connector at the sensor or ECM (C2 connector pin 23)
• Chafed wiring rubbing against the cylinder head or valve cover – a known wear point on this model
• ECM internal fault – rare, but possible on high-hour machines with previous electrical issues
• Aftermarket sensor incompatibility – incorrect resistance values if previously replaced with non-OEM parts

How to Troubleshoot and Fix Code 1351-3

Step 1: Visual Inspection Begin by locating the coolant temperature sensor on the engine block (driver's side, near thermostat housing). Inspect the connector for corrosion, bent pins, or coolant contamination. Check the wiring harness for obvious damage, particularly where it routes over the valve cover. On used machines, examine for previous repair attempts like electrical tape or spliced wires.

Step 2: Electrical Testing Disconnect the sensor connector and measure resistance across the sensor terminals using a digital multimeter (DMM). At 68°F (20°C), resistance should read approximately 2,400-2,700 ohms. At operating temperature (180°F/82°C), expect 300-350 ohms. A reading of infinite resistance (OL) confirms sensor failure. Also, check for sensor ground continuity to the engine block.

Step 3: Circuit Voltage Check With the sensor disconnected and ignition ON (engine off), measure voltage at the harness connector. You should see approximately 5.0 volts on the signal wire (reference voltage from ECM). If voltage is absent, trace the circuit back to the ECM C2 connector checking for breaks or shorts to ground.

Step 4: Connector and Harness Repair For used excavators, pay special attention to connector terminal tension. Spread female terminals slightly if connection is loose. Apply dielectric grease to prevent future corrosion. If wiring damage is found, repair using high-temperature automotive wire and heat-shrink connections—avoid crimp connectors in high-vibration areas.

Step 5: Component Replacement Replace the sensor with a genuine Hyundai or OEM-equivalent part (Hyundai P/N: 31Q4-40810). Torque to 18-22 ft-lbs and ensure the sensor probe fully contacts coolant. Clear codes using Hi-SCANPro diagnostic software or compatible scan tool, then test operation through a full heat cycle.

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Disclaimer: This guide provides general troubleshooting information. Always consult the Hyundai R455LC-7 service manual for complete specifications. If you're unfamiliar with electrical diagnostics or lack proper tools, consult a certified Hyundai heavy equipment technician to avoid further damage to expensive ECM components.