What is Hyundai HX220 NL EPFC Fault Code 168-5?

Fault Code 168-5 on the Hyundai HX220 NL EPFC indicates an electrical circuit issue with the engine coolant temperature sensor, specifically a "Data Valid but Below Normal Operational Range" condition. This code is triggered when the Engine Control Module (ECM) receives coolant temperature readings that are unusually low or erratic, suggesting sensor malfunction, wiring problems, or open circuits within the temperature monitoring system.

This fault is critical for the HX220's performance because the ECM relies on accurate coolant temperature data to optimize fuel injection timing, engine warm-up cycles, and hydraulic system efficiency. When this sensor provides incorrect readings, the excavator may experience poor fuel economy, rough idling, or delayed hydraulic response during cold starts.

Common Symptoms

• Check Engine Light or malfunction indicator illuminated on the dashboard
• Difficulty starting in cold weather or extended cranking times before engine fires
• Engine running in default mode with reduced power output or derate condition
• Hydraulic systems responding sluggishly during initial operation
• Abnormally high idle RPM as the ECM compensates for perceived "cold" engine conditions

Potential Causes

The most common technical causes for Code 168-5 on used Hyundai excavators include:

• Faulty coolant temperature sensor with internal resistance degradation (common after 5,000+ operating hours)
• Corroded or loose connector pins at the sensor harness connection point near the thermostat housing
• Damaged wiring harness due to rubbing against engine components or heat exposure from exhaust manifold proximity
• Open circuit or short to ground in the signal wire between the sensor and ECM
• ECM calibration issues or moisture intrusion in the engine control module itself (less common but possible in machines exposed to harsh environments)

How to Troubleshoot and Fix Code 168-5

Step 1: Visual Inspection Begin by locating the coolant temperature sensor on the cylinder head near the thermostat housing. Inspect the wiring harness for visible damage, chafing, or corrosion. On used excavators, pay special attention to areas where harnesses contact metal brackets or run near hot exhaust components.

Step 2: Electrical Testing Disconnect the sensor connector and use a digital multimeter to check sensor resistance. At room temperature (68°F/20°C), resistance should typically read between 2,000-3,000 ohms. Compare readings against Hyundai's specification chart. Also test for continuity between the sensor connector and ECM pins to identify open circuits.

Step 3: Signal Wire Verification With the sensor disconnected and ignition on, measure reference voltage at the harness connector (should read approximately 5 volts). Low or zero voltage indicates wiring issues or ECM problems. Check for shorts to ground by measuring resistance between signal wire and chassis ground.

Step 4: Component Replacement If sensor resistance is out of specification or the connector shows corrosion, replace the coolant temperature sensor with an OEM or equivalent part. Clean connector terminals with electrical contact cleaner before reassembly. Clear codes using Hyundai diagnostic software (Hi-MATE or compatible scanner) and verify repair through a complete warm-up cycle.

For used excavators, always inspect harness routing and secure any loose wiring away from heat sources to prevent recurrence.

---

Disclaimer: This guide provides general troubleshooting information. Always consult the official Hyundai service manual for your specific machine serial number and consider professional diagnostic assistance for complex electrical issues.