Hyundai HX220 NL EPFC Fault Code 105-1: Complete Diagnostic Guide

What is Hyundai HX220 NL EPFC Fault Code 105-1?

Fault Code 105-1 indicates a low voltage condition or open circuit in the intake air heater relay circuit of your Hyundai HX220 NL excavator. This diagnostic trouble code (DTC) is triggered when the Engine Control Module (ECM) detects abnormal electrical resistance or insufficient voltage supply to the intake air heater system, which is critical for cold-start performance in diesel engines.

The intake air heater (also called a grid heater or intake manifold heater) preheats incoming air during cold starts to ensure proper combustion. When the ECM cannot properly energize the heater relay due to circuit problems, code 105-1 stores in memory. For the HX220 NL's electronic fuel injection system, this malfunction can severely impact starting reliability in cold weather conditions and may trigger the machine into a protective derate mode.

Common Symptoms

Operators experiencing fault code 105-1 may notice:

• Difficult or extended cranking during cold starts, especially in temperatures below 40°F (4°C)
• Amber or red warning light illuminated on the instrument cluster with reduced engine power
• White or gray smoke during initial startup due to incomplete combustion
• Rough idle for the first few minutes after a cold start
• Engine derate mode limiting RPM to approximately 1800-2000 until the engine reaches operating temperature

Potential Causes

The most common technical failures triggering code 105-1 on used HX220 NL excavators include:

• Faulty intake air heater relay (relay coil resistance out of specification or contact points corroded)
• Damaged wiring harness between the ECM and heater relay, particularly at known rub points near the engine mount brackets
• Corroded or loose connector pins at the relay socket or ECM connection (common in machines with 5,000+ hours)
• Blown fuse in the intake heater power supply circuit
• Failed intake air heater element creating excessive current draw that damages the relay circuit
• ECM internal driver circuit failure (less common but possible in high-hour machines)

How to Troubleshoot and Fix Code 105-1

Step 1: Visual Inspection and Preliminary Checks

Begin by locating the intake air heater relay in the main fuse/relay box (typically mounted near the battery compartment). Inspect all wiring harnesses running from the ECM to the relay for obvious damage, chafing, or burn marks. On used excavators, pay special attention to harness routing near moving components or sharp edges where insulation wear commonly occurs. Check the relay fuse with a multimeter and replace if blown.

Step 2: Relay and Circuit Testing

Remove the intake air heater relay and test coil resistance using a digital multimeter. Typical relay coil resistance should read between 70-90 ohms (consult your service manual for exact specifications). Test for battery voltage (approximately 24V on this model) at the relay power supply terminal with ignition on. Inspect the relay socket for corrosion, bent pins, or moisture intrusion—common issues in machines operating in wet or dusty environments.

Step 3: Harness Continuity and ECM Signal Testing

With the relay removed, use your multimeter to check continuity between the ECM connector pin (refer to wiring diagram) and the relay control terminal. Resistance should be less than 5 ohms. Check for short circuits to ground by measuring resistance between the control wire and chassis ground (should read infinite/OL). If using Hyundai Hi-Mate diagnostic software, monitor the ECM's commanded state for the heater relay while cranking to verify the ECM is attempting activation.

Step 4: Component Replacement and Verification

If circuit testing confirms proper wiring, replace the intake air heater relay with an OEM or equivalent part. Before replacing the ECM (expensive and rarely the cause), verify the intake heater element itself isn't drawing excessive current by measuring amperage during activation—typical draw is 30-50 amps. After repairs, clear fault codes using diagnostic software and perform a cold-start test to verify proper operation.

Disclaimer: This guide provides general diagnostic procedures for fault code 105-1. Always consult the official Hyundai service manual for your specific serial number range and component specifications. If you're uncomfortable performing electrical diagnostics, consult a certified heavy equipment technician to avoid damaging expensive electronic components.