What is Hyundai HX220 NL EPFC Fault Code 4171 (5745-18)?

Fault Code 4171 (5745-18) indicates a malfunction in the Engine Control Module (ECM) communication circuit or a critical sensor input failure within the electronic fuel injection system. This diagnostic trouble code (DTC) specifically relates to the hydraulic pump control solenoid circuit or engine load sensor signal experiencing an abnormal voltage condition or complete signal loss on the Hyundai HX220 NL equipped with Electronic Positive Flow Control (EPFC).

This code is critical because the EPFC system actively manages hydraulic pump output based on engine load demands. When communication breaks down between the ECM and the pump control system, the excavator cannot properly regulate hydraulic flow, leading to inefficient operation, reduced performance, and potential engine protection mode activation. For used excavators, this fault often signals deteriorating electrical connections or aging sensors that compromise the machine's advanced fuel efficiency features.

Common Symptoms

• Engine derate mode activated, limiting maximum RPM to approximately 1,500-1,800 RPM to protect the drivetrain
• Amber warning light illuminated on the instrument cluster with reduced hydraulic response
• Sluggish hydraulic functions, particularly during combined operations (swing and boom movements simultaneously)
• Intermittent loss of power during heavy digging or lifting operations
• Diagnostic display showing error code 4171 or 5745-18 when accessed through the monitor panel

Potential Causes

The most common technical causes for Code 4171 on used HX220 NL excavators include:

• Corroded or loose connector pins at the engine harness connection point near the hydraulic pump (known wear point on machines with 4,000+ hours)
• Failed hydraulic pump pressure sensor providing incorrect load data to the ECM
• Damaged wiring harness due to rubbing against the engine block or hydraulic lines in the pump compartment
• ECM internal fault or corrupted calibration data (less common but possible in high-hour machines)
• Low battery voltage or poor ground connections affecting signal integrity throughout the electrical system
• Contaminated electrical connectors from hydraulic fluid leaks migrating into the engine bay wiring

How to Troubleshoot and Fix Code 4171 (5745-18)

Step 1: Visual Inspection and Connection Check Begin by disconnecting the battery and thoroughly inspecting all electrical connectors between the ECM and the hydraulic pump control solenoid. On used excavators, focus on the main engine harness connector located near the fuel injection pump—this is a known friction point. Look for green corrosion, bent pins, or hydraulic oil contamination. Clean connectors with electrical contact cleaner and apply dielectric grease.

Step 2: Voltage and Resistance Testing Using a digital multimeter, verify battery voltage (should be 12.0-12.6V with engine off). Check the ground circuit resistance from the ECM case to battery negative—it should read less than 0.5 ohms. Test the pump control solenoid circuit for continuity (typically 8-15 ohms resistance when disconnected). If readings are outside specifications, trace the harness for breaks or shorts.

Step 3: Sensor and Solenoid Verification Connect Hyundai Hi-MATE diagnostic software or compatible scan tool to access live data. Monitor the hydraulic pump pressure sensor output voltage (should vary between 0.5-4.5V under different loads). If signal is erratic or frozen, replace the sensor. Test the pump control solenoid operation using the software's actuator test function—you should hear audible clicks and see current flow.

Step 4: ECM Communication Test Verify CAN bus communication integrity between the ECM and instrument cluster. Check for additional fault codes that might indicate widespread electrical issues. For excavators with over 8,000 hours, consider ECM firmware updates available through authorized Hyundai dealers, as software patches address known EPFC control issues.

Important for Used Equipment: Before replacing expensive components like the ECM or hydraulic pump, thoroughly inspect all wire harness routing for chafing against metal edges, especially where harnesses pass through bulkheads. Many Code 4171 faults on used machines resolve with simple connector refurbishment and proper harness securing.

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Disclaimer: This guide provides general diagnostic information. Always consult the Hyundai HX220 NL service manual and consider professional assistance from certified Hyundai technicians for complex electrical diagnostics. Improper troubleshooting can cause additional damage to electronic components.