What is Hyundai HX220 NL EPFC Fault Code 4151 (5742-9)?

Fault Code 4151 (5742-9) indicates a malfunction in the Engine Controller Area Network (CAN) communication circuit, specifically related to abnormal voltage or signal disruption between the Engine Control Module (ECM) and the machine's main controller. This diagnostic trouble code (DTC) is triggered when the ECM detects inconsistent or missing data transmission on the CAN bus system that coordinates engine performance with hydraulic and electrical systems.

In the Hyundai HX220 NL EPFC excavator, this code is critical because the CAN communication network serves as the central nervous system linking the engine controller, display panel, and various sensors. When communication fails, the machine may enter derate mode or experience reduced performance to prevent potential damage. This fault is particularly common in used excavators where wiring harnesses have experienced years of vibration, moisture exposure, and thermal cycling.

Common Symptoms

• Warning lamp illumination on the instrument cluster, often accompanied by a check engine light or specific CAN communication error icon
• Engine power reduction or sudden derate mode activation, limiting machine performance to 70-80% capacity
• Intermittent gauge failures including erratic tachometer readings, fuel level fluctuations, or complete instrument cluster blackouts
• Difficulty starting or extended cranking times due to incomplete communication between starting system and ECM
• Error messages displayed on the monitor panel indicating "Controller Communication Error" or similar CAN-related warnings

Potential Causes

The most frequent causes of Code 4151 in used HX220 NL EPFC excavators include:

• Corroded or damaged CAN bus connectors at the ECM, particularly the 38-pin main harness connector prone to moisture intrusion
• Wiring harness chafing along the right-hand frame rail where the engine harness routes near hydraulic lines—a known wear point on this model
• Failed termination resistors (120-ohm resistors) at either end of the CAN network causing signal reflection
• ECM internal failure or corrupted software, more common in machines with 8,000+ operating hours
• Voltage supply issues from the main power distribution module affecting CAN bus voltage (should be 2.5V nominal)
• Aftermarket component interference from improperly installed accessories that disrupt CAN communication protocols

How to Troubleshoot and Fix Code 4151 (5742-9)

Step 1: Visual Inspection and Connector Check Begin by inspecting all CAN bus connectors starting at the ECM location (typically mounted on the right side of engine block). Disconnect the main 38-pin ECM connector and examine pins for corrosion, bent contacts, or green oxidation. Check the engine harness routing along the frame rail for obvious abrasion points where insulation may be worn through. Pay special attention to areas where the harness contacts metal edges or passes near the hydraulic pump—this is a documented wear point on used HX220 models.

Step 2: CAN Bus Voltage and Resistance Testing Using a digital multimeter (DMM), backprobe the CAN-High and CAN-Low wires at the ECM connector with the key in the ON position (engine off). You should measure approximately 2.5V on CAN-High and 2.5V on CAN-Low relative to ground. The voltage difference between the two should be near zero at rest. Next, disconnect both ends of the CAN network and measure resistance between CAN-High and CAN-Low—you should read approximately 60 ohms (two 120-ohm termination resistors in parallel). A reading of 120 ohms indicates one termination resistor has failed; infinite resistance suggests an open circuit in the network.

Step 3: Advanced Diagnostics with Factory Software Connect Hyundai Hi-Mate diagnostic software or compatible scan tool to the machine's diagnostic port. Monitor live CAN bus data while wiggling harness sections to identify intermittent faults. Check for ECM software version—early HX220 NL EPFC models may require firmware updates to address known CAN communication bugs. Clear the fault code and perform a stationary regeneration test while monitoring for code recurrence. For used excavators, verify no aftermarket devices (GPS trackers, telematics) are causing bus conflicts by temporarily disconnecting non-OEM components.

Critical for Used Machinery: Before replacing the ECM (a $2,000-$3,500 part), always verify harness integrity and connector condition. Approximately 75% of CAN communication faults in used excavators stem from wiring issues rather than controller failure. Consider applying dielectric grease to all CAN connectors during reassembly to prevent future corrosion.

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Disclaimer: This guide provides general troubleshooting information for Code 4151 (5742-9). Always consult the official Hyundai service manual for your specific machine serial number and consider professional diagnostic assistance for complex electrical issues. Improper repairs to CAN bus systems may cause additional fault codes or machine damage.