Hyundai R275LVS Fault Code 108-4: Complete Diagnostic Guide

What is Hyundai R275LVS Fault Code 108-4?

Fault Code 108-4 indicates an abnormal voltage condition in the hydraulic oil temperature sensor circuit, specifically a voltage signal that is too high or out of the expected range. This code is triggered when the Engine Control Module (ECM) detects a resistance value or voltage reading from the hydraulic oil temperature sensor that exceeds the manufacturer's predetermined threshold, typically above 4.5 volts.

This fault is critical for the R275LVS because the hydraulic system relies on accurate temperature monitoring to prevent overheating, maintain proper viscosity for component lubrication, and protect expensive hydraulic pumps and motors. When the ECM cannot accurately read hydraulic oil temperature, it may initiate protective measures that limit machine performance or trigger automatic shutdowns.

Common Symptoms

When Code 108-4 is active on your Hyundai R275LVS, operators typically experience:

• Warning light or malfunction indicator illuminated on the instrument cluster, often accompanied by a temperature gauge reading abnormally low or pegged at minimum
• Reduced hydraulic performance or speed limitations as the ECM enters a protective derate mode
• Intermittent loss of hydraulic power, especially during cold starts when actual oil temperature is low
• Fan running continuously at high speed, as the system assumes worst-case temperature scenarios
• Error messages displayed on the monitor panel indicating hydraulic system malfunction

Potential Causes

The most common technical failures causing Code 108-4 in used R275LVS excavators include:

• Open circuit in the sensor wiring harness, often caused by wire breakage near flex points around the hydraulic tank or pump mounting areas
• Failed hydraulic oil temperature sensor with internal open circuit condition (common failure mode after 5,000+ operating hours)
• Corroded or damaged connector pins at the sensor plug or ECM harness connection, particularly in machines operated in wet or corrosive environments
• Harness chafing against sharp edges near the hydraulic tank mounting brackets—a known wear point on this model
• ECM internal fault (rare, but possible in higher-hour machines with electrical system history)

How to Troubleshoot and Fix Code 108-4

Step 1: Visual Inspection Begin by locating the hydraulic oil temperature sensor on the hydraulic tank (typically mounted on the side or return line filter housing). Inspect the sensor connector for corrosion, bent pins, oil contamination, or moisture intrusion. On used excavators, check the entire wiring harness route from sensor to ECM for signs of rubbing, particularly where the harness passes near hydraulic lines or structural components.

Step 2: Electrical Testing Disconnect the sensor connector and use a digital multimeter to measure resistance across the sensor terminals. At approximately 20°C (68°F), resistance should read between 2,000-3,000 ohms (consult your service manual for exact specifications). An open circuit (infinite resistance) confirms sensor failure. Next, check the harness side: with ignition on and sensor disconnected, measure voltage at the signal wire—you should see approximately 5 volts (reference voltage from the ECM).

Step 3: Harness Continuity Check With the sensor disconnected and ignition off, check continuity between the sensor connector pins and the corresponding ECM pins (refer to wiring diagrams in your technical manual). Any open circuit indicates harness damage. For used machines, pay special attention to connector backprobing to check for intermittent connections caused by terminal tension loss.

Step 4: Component Replacement and Verification If the sensor tests faulty, replace it with a genuine Hyundai part or quality OEM equivalent, ensuring proper thread sealant application. After replacement, clear codes using Hi-MATE diagnostic software or equivalent Hyundai service tool, and verify the fault does not return. If the harness shows damage, repair with proper gauge wire and protect with abrasion-resistant sleeving before routing away from wear points.

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Disclaimer: This guide provides general diagnostic information for experienced technicians. Always consult the official Hyundai service manual for your specific serial number and follow proper safety procedures. If you're uncertain about electrical diagnostics on used excavators, consult a certified Hyundai technician to avoid damage to expensive electronic components.