What is Hyundai R805LC-7 Fault Code 1351-4?

Fault Code 1351-4 on the Hyundai R805LC-7 excavator indicates a "Swing Motor Oil Temperature Sensor - Voltage Below Normal" condition. This diagnostic trouble code (DTC) is triggered when the Engine Control Module (ECM) detects an abnormally low voltage signal from the swing motor oil temperature sensor, typically below the manufacturer's specified threshold of approximately 0.5 volts.

The swing motor oil temperature sensor is a critical component in the hydraulic swing system that monitors operating temperatures to prevent thermal damage and ensure optimal performance. On the R805LC-7, this sensor provides real-time data to the ECM, which regulates hydraulic flow and protects components from overheating. When voltage readings fall outside normal parameters, the system assumes a sensor or circuit fault, compromising thermal protection and potentially leading to swing motor damage if left unresolved.

Common Symptoms

When Code 1351-4 is active on your Hyundai R805LC-7, you may experience:

• Warning light illumination on the instrument cluster, specifically the engine or hydraulic system indicator
• Erratic swing speed control or inconsistent swing motor performance during operation
• False temperature readings displayed on the monitor panel, often showing extremely low or no temperature
• Reduced swing function or activation of derate mode limiting swing motor output
• Intermittent code triggering, especially during cold starts or initial operation after long shutdown periods

Potential Causes

The most common technical causes for fault code 1351-4 on used R805LC-7 excavators include:

• Damaged or corroded sensor wiring harness, particularly at common rub points near the swing bearing race or center joint
• Failed swing motor oil temperature sensor due to internal short circuit or component degradation from prolonged exposure to heat and hydraulic fluid contamination
• Poor electrical connections at the sensor connector, often caused by moisture intrusion, corrosion, or loose terminal pins
• Wiring harness chafing against the swing motor housing or hydraulic lines, creating intermittent shorts to ground
• ECM internal circuit failure (rare) affecting the sensor input channel
• Previous repair attempts using incorrect sensor specifications or improper wire splicing techniques

How to Troubleshoot and Fix Code 1351-4

Step 1: Visual Inspection of Sensor and Wiring Begin by locating the swing motor oil temperature sensor on the swing motor assembly. Thoroughly inspect the sensor connector for corrosion, bent pins, moisture, or oil contamination. On used excavators, pay special attention to the wiring harness routing from the sensor to the main harness—check for visible wear, chafing against metal surfaces, or damage from hydraulic hose movement near the swing bearing area.

Step 2: Electrical Testing with Multimeter Disconnect the sensor connector and use a digital multimeter to measure resistance across the sensor terminals. At room temperature (20°C/68°F), resistance should typically read between 2,000-3,000 ohms (consult your service manual for exact specifications). Next, measure voltage supply at the harness connector with ignition on—you should see approximately 5 volts reference voltage from the ECM. If voltage is absent or incorrect, trace the harness for breaks or shorts to ground.

Step 3: Sensor Replacement and Harness Repair If the sensor fails resistance testing or the harness shows continuity faults, replace the swing motor oil temperature sensor with a genuine Hyundai part (part number should be verified through dealer). Before installation, clean the sensor mounting bore and apply appropriate thread sealant. For harness damage common in used machines, repair using proper gauge wire and heat-shrink connectors, ensuring routing avoids future friction points. After repairs, clear codes using Hi-Scan Pro or compatible diagnostic software and perform a swing motor function test to verify proper temperature readings.

Disclaimer: This guide provides general troubleshooting information. Always consult the official Hyundai R805LC-7 service manual and consider professional diagnostic assistance for complex electrical issues or if you lack proper tools and training.