What is Hyundai R805LC-7 Fault Code 167-18?

Fault Code 167-18 on the Hyundai R805LC-7 excavator indicates a "Transmission Oil Temperature Sensor Circuit High Voltage" condition. This diagnostic trouble code (DTC) is triggered when the Electronic Control Module (ECM) detects an abnormally high voltage signal from the transmission oil temperature sensor, typically above 4.5-4.8 volts, exceeding the manufacturer's calibrated threshold.

This code is critical because the transmission oil temperature directly affects hydraulic system performance, component longevity, and operator safety. The ECM uses this sensor data to manage transmission operation, cooling fan engagement, and protective derate modes. On used R805LC-7 excavators, this fault can lead to inadequate thermal protection, potentially causing catastrophic transmission damage if ignored.

Common Symptoms

• Transmission overheat warning light illuminated on the instrument panel
• Reduced hydraulic response or sluggish boom/bucket movements due to ECM entering protective mode
• Cooling fan running continuously at maximum speed regardless of actual oil temperature
• Intermittent or persistent fault code stored in ECM memory, even after key cycles
• Transmission temperature gauge reading incorrectly low or not responding

Potential Causes

The most common technical causes for Code 167-18 on used Hyundai excavators include:

• Open circuit or broken wire in the sensor harness, particularly near flex points around the transmission housing
• Corroded or damaged connector pins at the sensor or ECM connection points—extremely common on machines operating in wet or coastal environments
• Failed transmission oil temperature sensor with internal open circuit or degraded thermistor element
• Chafed wiring harness rubbing against the transmission case or frame rails (known wear point on R805LC-7 models)
• ECM internal circuit failure (rare, but possible on high-hour machines)
• Poor ground connection at sensor or ECM grounding points

How to Troubleshoot and Fix Code 167-18

Step 1: Visual Inspection Begin by inspecting the transmission oil temperature sensor located on the transmission housing. Check the wiring harness from the sensor to the ECM for visible damage, chafing, or corrosion. On used excavators, pay special attention to harness routing near moving components and areas exposed to hydraulic fluid or debris.

Step 2: Connector and Resistance Testing Disconnect the sensor connector and inspect for bent pins, moisture, or corrosion. Clean with electrical contact cleaner if necessary. Using a digital multimeter, measure the sensor resistance at various temperatures. A typical NTC sensor should read approximately 2,000-3,000 ohms at room temperature. Compare readings to Hyundai's specifications.

Step 3: Circuit Voltage Testing With the sensor disconnected and ignition on, measure voltage at the ECM side of the harness connector. You should see approximately 5 volts reference voltage. If voltage reads close to battery voltage (12-24V), this confirms an open circuit in the sensor ground path or signal wire.

Step 4: Harness Continuity Check Test continuity between the sensor connector and ECM pins using wiring diagrams specific to the R805LC-7. Check for shorts to voltage, shorts to ground, and proper signal wire integrity. For used machines, probe connections at multiple points along the harness to identify intermittent breaks.

Step 5: Component Replacement If testing confirms sensor failure, replace with a genuine Hyundai or OEM-equivalent temperature sensor. Ensure proper torque specifications (typically 15-20 Nm) and apply thread sealant. After harness or sensor replacement, clear codes using Hyundai Hi-MATE diagnostic software and perform a test cycle.

---

Disclaimer: This guide provides general troubleshooting information for experienced diesel mechanics. Always consult the official Hyundai R805LC-7 service manual and consider professional diagnostic assistance for complex electrical issues, especially on used equipment with unknown maintenance history.