What is Hyundai Excavator Fault Code 108-1?

Fault Code 108-1 indicates an abnormal voltage signal detected in the Engine Coolant Temperature (ECT) Sensor Circuit, specifically registering a high voltage or open circuit condition. This diagnostic trouble code (DTC) is generated when the Electronic Control Module (ECM) receives a voltage reading above the manufacturer's specified threshold from the coolant temperature sensor circuit, typically exceeding 4.5-4.8 volts.

The ECT sensor plays a critical role in Hyundai excavators by monitoring engine operating temperature and sending real-time data to the ECM. This information directly influences fuel injection timing, idle speed control, and engine protection protocols. When this sensor circuit malfunctions, the ECM cannot accurately determine engine temperature, potentially leading to improper fuel delivery, increased emissions, and inadequate engine protection against overheating.

Common Symptoms

• Check Engine Light or Engine Warning Lamp illuminated on the instrument cluster
• Engine runs in default/limp mode with reduced power output and RPM limitations
• Hard starting conditions, especially during cold weather operation
• Excessive black smoke from exhaust due to rich fuel mixture from incorrect temperature readings
• Cooling fan may run continuously at full speed regardless of actual engine temperature

Potential Causes

The most frequent causes of Code 108-1 on used Hyundai excavators include:

• Open circuit in the ECT sensor wiring harness, commonly caused by wire breaks near engine mounting points where vibration and flexing occur
• Failed ECT sensor with internal circuit breakdown (common in machines with 5,000+ operating hours)
• Corroded or loose connector pins at the sensor plug or ECM connector, particularly on machines exposed to harsh environmental conditions
• Damaged wiring insulation from rubbing against engine components, exhaust manifolds, or frame edges
• Poor ground connection in the sensor circuit reference wire
• ECM internal fault (rare, but possible in older machines with moisture intrusion history)

How to Troubleshoot and Fix Code 108-1

Step 1: Visual Inspection Begin by inspecting the ECT sensor located on the engine block (typically near the thermostat housing). Check the wiring harness for obvious damage, cuts, or abrasion points. On used excavators, pay special attention to areas where harnesses pass near moving components or sharp edges. Examine the connector for corrosion, pushed-back pins, or moisture contamination.

Step 2: Sensor and Circuit Testing Disconnect the ECT sensor connector and measure resistance across the sensor terminals using a digital multimeter. At room temperature (20°C/68°F), resistance should typically read 2,000-3,000 ohms (consult your service manual for exact specifications). Next, check for continuity between each sensor wire and the ECM connector. Measure voltage at the ECM side with the key on, engine off—you should see approximately 5 volts reference voltage on the signal wire.

Step 3: Connector and Harness Repair If voltage readings are correct but the sensor tests faulty, replace the ECT sensor with a genuine or OEM-equivalent part. If you find open circuits or damaged wiring (common in older machines), repair or replace the affected harness section. Clean all connector terminals with electrical contact cleaner and apply dielectric grease to prevent future corrosion. After repairs, clear the fault code using Hyundai diagnostic software or a compatible scan tool and verify the code does not return.

Disclaimer: This guide provides general troubleshooting information. Always consult your machine's service manual and consider professional diagnostic assistance for complex electrical issues or if you're unfamiliar with excavator electrical systems.