What is Hyundai R335LC-9T Fault Code 167-1?

Fault Code 167-1 on the Hyundai R335LC-9T excavator indicates a "Hydraulic Oil Temperature Sensor Circuit - Data Valid But Below Normal Operating Range (Low Voltage)." This fault occurs when the Engine Control Module (ECM) or Integrated Control Unit (ICU) detects an abnormally low voltage signal from the hydraulic oil temperature sensor, typically below 0.5 volts.

This code affects the hydraulic system monitoring circuit, which is critical for protecting the R335LC-9T's main hydraulic pump and valve assemblies. The sensor measures hydraulic oil temperature to prevent overheating damage and optimize hydraulic performance. When this circuit fails, the machine cannot accurately monitor oil temperature, potentially leading to inadequate warm-up procedures or undetected overheating conditions that can severely damage expensive hydraulic components.

Common Symptoms

• Warning light illuminated on the instrument panel, often accompanied by a wrench or service icon
• Hydraulic system derate or reduced hydraulic flow, especially during cold starts when the system relies on accurate temperature readings
• Intermittent or constant fault code display on the digital monitor
• Machine may enter limp mode preventing full operational capability until the issue is resolved
• Abnormal hydraulic warm-up behavior, with the system not adjusting flow rates appropriately for temperature conditions

Potential Causes

The most common causes for Code 167-1 on used R335LC-9T excavators include:

• Failed hydraulic oil temperature sensor due to internal resistance breakdown (common after 5,000+ operating hours)
• Open circuit or broken wire in the sensor harness, particularly at known friction points near the hydraulic tank mounting bracket
• Corroded or loose connector pins at the sensor connection or ECM/ICU harness interface
• Damaged sensor wiring caused by chafing against the main hydraulic tank or undercarriage components during long-term operation
• ECM/ICU internal circuit failure (less common, but possible in high-hour machines)
• Poor ground connection at the sensor mounting point due to paint buildup or corrosion on used equipment

How to Troubleshoot and Fix Code 167-1

Step 1: Visual Inspection Begin with a thorough visual inspection of the hydraulic oil temperature sensor located on the hydraulic oil tank. Check the sensor connector for corrosion, bent pins, or oil contamination. On used excavators, examine the entire wiring harness from the sensor to the ICU for signs of rubbing, cuts, or heat damage—particularly where the harness routes near moving components.

Step 2: Electrical Testing Disconnect the sensor and use a digital multimeter to measure sensor resistance. At room temperature (20°C/68°F), resistance should typically be 2,000-3,000 ohms (consult your service manual for exact specifications). Next, check for continuity in the harness between the sensor connector and the ECM/ICU. Measure voltage supply at the sensor connector with the key on, engine off—you should see approximately 5 volts reference voltage from the control module.

Step 3: Ground and Circuit Verification Verify a clean ground connection at the sensor mounting location. On used machines, remove the sensor, clean the mounting threads, and ensure bare metal contact. Check for short circuits to ground using the multimeter's continuity function with the harness disconnected at both ends.

Step 4: Component Replacement If testing confirms sensor failure, replace with a genuine Hyundai sensor or quality OEM equivalent. For used excavators, always replace the connector pigtail simultaneously if any corrosion is present, as this prevents repeat failures. Clear the code using Hi-Mate diagnostic software or appropriate scan tool and verify proper operation through a complete heat cycle.

Step 5: System Verification After repairs, monitor the live data stream from the temperature sensor to confirm voltage changes appropriately with temperature (voltage should decrease as temperature increases with NTC thermistor design). Operate the machine through normal working temperature range and verify the code does not return.

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Disclaimer: This guide provides general troubleshooting information for experienced technicians. Always consult the official Hyundai service manual for your specific serial number range and follow all safety procedures. If you're unfamiliar with electrical diagnostics or working with hydraulic systems, consult a certified Hyundai excavator technician to prevent equipment damage or personal injury.