Hyundai HX220 NL EPFC Fault Code 4957 (520750-31): Meaning and Fix

What is Hyundai HX220 NL EPFC Fault Code 4957 (520750-31)?

Fault Code 4957 (520750-31) indicates a malfunction in the hydraulic pump solenoid valve circuit, specifically detecting an abnormal voltage or open circuit condition in the main pump control system. This code is triggered when the Electronic Control Module (ECM) detects that the electrical signal to the hydraulic pump's proportional solenoid valve is outside the expected range, typically between 0.5-4.5 volts.

This fault is critical for the HX220 NL EPFC because the proportional solenoid valve directly controls hydraulic pump displacement and flow rate. When this circuit fails, the excavator cannot properly regulate hydraulic pressure, leading to reduced performance or complete loss of hydraulic functions. In used machines, this code often appears due to wiring degradation rather than actual solenoid failure.

Common Symptoms

• Hydraulic system derate – reduced boom, arm, or swing speed even at full throttle
• Intermittent loss of hydraulic power during operation, especially when the machine is hot
• Warning light illumination on the instrument cluster with possible audible alarm
• Erratic hydraulic response – jerky movements or inconsistent control feel
• Engine may enter limp mode limiting RPM to protect the system

Potential Causes

The most common technical causes for Code 4957 on used HX220 excavators include:

• Damaged wiring harness between the ECM and pump solenoid valve, particularly at flex points near the pump mounting area where vibration causes wire chafing
• Corroded or loose connector pins at the solenoid valve plug (common in machines operating in wet or corrosive environments)
• Failed proportional solenoid valve due to internal coil breakdown or mechanical seizure from contaminated hydraulic oil
• ECM internal driver circuit failure (less common but possible in high-hour machines)
• Poor ground connection at the pump assembly or ECM mounting points

How to Troubleshoot and Fix Code 4957 (520750-31)

Step 1: Visual Inspection
Inspect the wiring harness from the ECM to the hydraulic pump solenoid valve. On used excavators, check for wire insulation damage at known rub points—especially where the harness passes through the engine bay bulkhead and near the pump mounting bracket. Look for green corrosion on connector pins and ensure the connector lock is fully engaged.

Step 2: Electrical Testing
Using a digital multimeter, disconnect the solenoid valve connector and measure resistance across the solenoid coil terminals. Typical resistance should be 3-8 ohms (consult service manual for exact spec). Next, check for supply voltage at the harness side with ignition on—you should see battery voltage (12-14V). Measure ground continuity from the solenoid ground pin to chassis ground; resistance should be less than 1 ohm.

Step 3: Signal Testing with Diagnostic Software
Connect Hyundai Hi-MATE or compatible diagnostic software to monitor real-time solenoid command values from the ECM. Command the solenoid through the software while measuring actual voltage at the valve connector with your multimeter. If commanded voltage doesn't match actual voltage, the issue is in the harness or ECM driver circuit. If they match but the code persists, replace the solenoid valve.

Step 4: Repair and Verification
For harness damage, repair using OEM-spec wire and heat-shrink connectors—avoid crimp splices in high-vibration areas. Clean corroded connectors with electrical contact cleaner and apply dielectric grease. After repairs, clear the fault code and operate the machine through a full work cycle to verify the fix holds under load.

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Disclaimer: This guide provides general troubleshooting information. Always consult the manufacturer's service manual for your specific machine serial number and software version. If you're unfamiliar with electrical diagnostics or hydraulic systems, consult a certified Hyundai heavy equipment technician to avoid injury or further damage.