What is Hyundai R275LC-9T Fault Code 108-2?

Fault Code 108-2 on the Hyundai R275LC-9T excavator indicates an intermittent or invalid signal from the Engine Coolant Temperature (ECT) Sensor circuit. This code is classified as a "2" severity level, meaning the sensor signal is erratic or falls outside the expected voltage range but hasn't completely failed.

The ECT sensor monitors coolant temperature and sends critical data to the Engine Control Module (ECM), which uses this information to adjust fuel injection timing, throttle response, and cooling fan operation. On the R275LC-9T equipped with a Cummins QSB6.7 or similar engine, accurate coolant temperature readings are essential for preventing overheating, optimizing fuel efficiency, and maintaining proper hydraulic oil temperatures during heavy digging operations.

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Common Symptoms

Operators may experience the following when Code 108-2 is active:

• Check Engine Light or warning symbol illuminated on the instrument cluster
• Erratic temperature gauge readings that fluctuate unusually or show intermittent spikes
• Hard starting when the engine is cold, as the ECM cannot properly enrich the fuel mixture
• Reduced engine power or derate mode activation if the ECM defaults to fail-safe parameters
• Cooling fan running continuously at high speed, even when the engine is cool

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Potential Causes

The most common technical causes for Code 108-2 on used R275LC-9T excavators include:

• Corroded or loose wiring connections at the ECT sensor connector (common in machines with 5,000+ operating hours)
• Damaged sensor harness due to vibration or rubbing against the engine block near the thermostat housing
• Failing ECT sensor with internal resistance degradation, causing intermittent signal dropout
• ECM grounding issues or poor chassis ground connections affecting sensor reference voltage
• Coolant contamination or air pockets around the sensor tip preventing accurate temperature readings
• Worn connector pins or moisture ingress in the sensor plug (typical in machines operating in wet conditions)

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How to Troubleshoot and Fix Code 108-2

Step 1: Visual Inspection
Locate the ECT sensor on the engine block (typically near the thermostat housing on Cummins engines). Inspect the wiring harness for abrasion, melted insulation, or contact with hot engine components. Check the sensor connector for corrosion, bent pins, or moisture—common issues in used excavators.

Step 2: Test Sensor Resistance
Disconnect the ECT sensor connector. Using a digital multimeter, measure resistance across the sensor terminals. At room temperature (68°F/20°C), resistance should read approximately 2,000-3,000 ohms. Compare readings against the manufacturer's temperature-resistance chart. Erratic or out-of-spec readings indicate sensor replacement is needed.

Step 3: Check Circuit Voltage
With the ignition on (engine off), measure reference voltage at the harness connector. You should see approximately 5 volts on the signal wire. If voltage is absent or fluctuates, trace the harness back to the ECM checking for breaks, shorts to ground, or damaged insulation at known rub points near engine mounts.

Step 4: Verify Ground Integrity
Test the ground circuit continuity between the sensor ground pin and chassis ground. Resistance should be less than 1 ohm. Clean all ground terminals and ECM mounting points, as corroded grounds are a frequent cause in older machines.

Step 5: Clear Code and Test
After repairs, use Hyundai Hi-MATE diagnostic software or a compatible scan tool to clear the fault code. Operate the machine through a complete heat cycle, monitoring live data to confirm stable sensor readings between 180-220°F during normal operation.

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Disclaimer: This guide provides general troubleshooting information. Always consult the Hyundai R275LC-9T service manual and consider professional diagnostic assistance for complex electrical issues. Improper repairs may void warranties or cause equipment damage.