What is Hyundai HX220 NL EPFC Fault Code 3571 (4334-3)?

Fault Code 3571 (4334-3) indicates a malfunction in the Engine Preheating System Circuit, specifically related to the glow plug relay or intake air heater control circuit. This diagnostic trouble code (DTC) is triggered when the Electronic Control Module (ECM) detects an abnormal voltage, open circuit, or short circuit in the preheating system that prepares the diesel engine for cold starts.

In the Hyundai HX220 NL EPFC excavator, this system is critical for proper combustion during startup, especially in cold weather conditions. The preheating system ensures adequate cylinder temperatures for reliable ignition of diesel fuel. When this code appears, the ECM has identified that the commanded circuit voltage does not match expected parameters, compromising cold-start reliability and potentially affecting engine longevity through incomplete combustion cycles.

Common Symptoms

• Glow plug warning light illuminated on the instrument cluster, often flashing or remaining solid
• Difficult or prolonged cranking during cold starts, particularly in temperatures below 50°F (10°C)
• Rough idle or excessive white smoke immediately after startup indicating incomplete combustion
• Engine derate mode may activate in severe cases, limiting power output to protect engine components
• Stored fault code in ECM memory even if engine eventually starts and runs normally

Potential Causes

The most common technical failures triggering Code 3571 in used HX220 excavators include:

• Glow plug relay failure due to contact wear or coil burnout from repeated thermal cycling
• Damaged or corroded wiring harness between the ECM and preheater relay, especially at connection points near the engine block where vibration and heat cause insulation breakdown
• Failed intake air heater element or grid heater with internal short circuit
• Corroded or loose connector pins at the relay socket—a frequent issue in machines operating in wet or coastal environments
• ECM internal driver circuit failure, though less common, can occur in high-hour machines (over 8,000 hours)
• Blown fuse in the preheating circuit power supply

How to Troubleshoot and Fix Code 3571 (4334-3)

Step 1: Visual Inspection Begin by locating the glow plug relay (typically mounted on the firewall or fuse panel). Inspect all connectors for corrosion, bent pins, or moisture intrusion. Check the wiring harness for chafing points where it contacts the engine block or frame—a known wear point on used excavators.

Step 2: Electrical Testing Using a digital multimeter, verify relay operation. With ignition on (engine off), check for battery voltage (12V) at the relay power supply terminal. Test relay coil resistance (should read 70-90 ohms typically). Activate the preheating system and verify the relay clicks and provides voltage output to the heater circuit.

Step 3: Circuit Continuity Check Disconnect the intake air heater connector and measure resistance. A functioning heater typically shows 0.5-2.0 ohms. Infinite resistance indicates an open circuit; near-zero resistance suggests a short. Inspect the harness between ECM pin 47 (verify in service manual) and the relay for continuity and proper insulation resistance to ground (should exceed 10k ohms).

Step 4: Component Replacement For used excavators, replace the glow plug relay first as it's the most common failure point and relatively inexpensive. If symptoms persist, test and replace the intake air heater element. Always apply dielectric grease to connectors during reassembly to prevent future corrosion.

Step 5: Clear Codes and Verify Use Hyundai Hi-MATE diagnostic software or compatible scan tool to clear the fault code. Perform a cold start test cycle to confirm proper preheating operation and verify no code recurrence.

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Disclaimer: This guide provides general troubleshooting information for educational purposes. Always consult the official Hyundai service manual for your specific machine serial number and torque specifications. If unfamiliar with high-voltage electrical systems or lacking proper diagnostic tools, seek assistance from a certified Hyundai excavator technician to avoid equipment damage or personal injury.