Hyundai R505LC-7 Fault Code 718-11: Complete Diagnostic Guide

What is Hyundai R505LC-7 Fault Code 718-11?

Fault Code 718-11 indicates a hydraulic oil temperature sensor voltage is too low or the circuit has detected a short to ground. This diagnostic trouble code (DTC) is generated when the Engine Control Module (ECM) receives abnormally low voltage readings from the hydraulic oil temperature sensor, typically below 0.3 volts for more than 2 seconds.

The hydraulic oil temperature sensor on the R505LC-7 monitors the operating temperature of the hydraulic system, which is critical for protecting hydraulic pumps, motors, and cylinder seals. When this sensor fails or provides inaccurate readings, the machine's ECM cannot properly regulate hydraulic fan speeds or provide overheat warnings, potentially leading to catastrophic hydraulic system damage on these 50-ton class excavators.

Common Symptoms

When Code 718-11 is active, operators typically experience:

• Hydraulic overheat warning light illuminated on the instrument cluster, even when oil temperature feels normal
• Hydraulic cooling fan running continuously at high speed, regardless of actual oil temperature
• Reduced hydraulic performance or machine entering derate mode to protect components
• Erratic temperature gauge readings or gauge stuck at minimum position
• Secondary fault codes may appear related to hydraulic system performance (700-series codes)

Potential Causes

The most common technical causes for Code 718-11 on used R505LC-7 excavators include:

• Damaged or corroded sensor connector at the hydraulic tank – this connector is exposed to moisture and debris
• Wiring harness chafing where the sensor cable passes near the swing motor or along the frame rail (known wear point)
• Failed hydraulic oil temperature sensor due to internal short circuit or contamination
• Corroded pins in the 3-pin Deutsch connector between sensor and main harness
• ECM internal fault (rare, but possible on high-hour machines)
• Aftermarket sensor incompatibility if sensor was previously replaced with non-OEM parts

How to Troubleshoot and Fix Code 718-11

Step 1: Visual Inspection Begin by locating the hydraulic oil temperature sensor mounted on the left side of the hydraulic tank. Inspect the wiring harness for obvious damage, including cuts, abrasions, or oil contamination. On used excavators, check specifically where the harness routes under the swing bearing – this is a common friction point that causes wire insulation failure.

Step 2: Connector Testing Disconnect the 3-pin sensor connector and inspect for corrosion, bent pins, or moisture intrusion. Clean connector pins with electrical contact cleaner and verify pin integrity. Check for approximately 2,500 ohms resistance across sensor terminals at room temperature using a digital multimeter (DMM).

Step 3: Circuit Voltage Check With the connector still disconnected and ignition ON (engine off), measure voltage at the ECM supply wire (typically pin 1) – you should read approximately 5 volts. If voltage is absent, trace the harness back toward the ECM for breaks or shorts.

Step 4: Ground Circuit Verification Test continuity between the sensor ground wire (typically pin 3) and chassis ground. Resistance should be less than 5 ohms. High resistance indicates corroded ground connections at the ECM or chassis grounding points.

Step 5: Sensor Replacement and Calibration If all circuits test correctly but the sensor shows incorrect resistance values, replace with a genuine Hyundai sensor (Part Number 31EH-42110 or equivalent). After installation, clear codes using Hi-MATE diagnostic software or an aftermarket scanner compatible with Hyundai protocols, then perform a cold-to-warm temperature verification test.

Critical for Used Machines: Before replacing any components, thoroughly inspect harness routing and secure any loose wiring that may contact moving parts. Many 718-11 codes on older R505LC-7 excavators are intermittent due to vibration-induced connector issues rather than actual sensor failure.

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Disclaimer: This guide provides general diagnostic information. Always consult the official Hyundai service manual for your specific machine serial number and consider professional diagnosis for complex electrical issues. Improper repairs can void warranties or create safety hazards.