Hyundai HX220 NL EPFC Fault Code 3717 (3226-13): Meaning and Fix

What is Hyundai HX220 NL EPFC Fault Code 3717 (3226-13)?

Fault Code 3717 (3226-13) indicates a malfunction in the engine coolant temperature sensor circuit, specifically detecting an abnormal voltage signal or open circuit condition in the ECM (Engine Control Module) monitoring system.

This code triggers when the ECM detects that the coolant temperature sensor is sending voltage readings outside the expected range—either too high (open circuit) or too low (short circuit). For the Hyundai HX220 NL equipped with the EPFC (Electronic Pump Flow Control) system, accurate coolant temperature data is critical. The ECM uses this information to adjust fuel injection timing, control engine warm-up cycles, and prevent overheating. When this sensor fails, the engine may enter a protective derate mode, limiting power output to prevent potential damage.

Common Symptoms

• Engine warning light illuminated on the instrument cluster (amber or red depending on severity)
• Reduced engine power or derate mode activation, limiting hydraulic performance
• Hard starting or extended cranking time, especially in cold conditions
• Rough idle or irregular engine RPM during warm-up phase
• Cooling fan running continuously at high speed regardless of actual engine temperature

Potential Causes

The most common technical causes for Code 3717 in used Hyundai excavators include:

• Coolant temperature sensor failure due to internal element degradation (common after 5,000+ operating hours)
• Wiring harness damage at known rub points near the engine block or along the frame rail where vibration causes insulation wear
• Corroded or loose connector pins at the sensor plug, especially on machines operated in wet or marine environments
• ECM internal fault (less common but possible in high-hour machines with electrical system stress)
• Damaged sensor mounting threads causing poor thermal contact with coolant passages

How to Troubleshoot and Fix Code 3717 (3226-13)

Step 1: Visual Inspection
Locate the coolant temperature sensor on the engine block (typically near the thermostat housing). Inspect the wiring harness for visible damage, chafing, or oil contamination. Check the connector for corrosion, bent pins, or moisture intrusion—common issues in used excavators.

Step 2: Electrical Testing
Disconnect the sensor and use a digital multimeter to measure resistance across the sensor terminals. At room temperature (20°C/68°F), resistance should typically read 2,000-3,000 ohms (consult Hyundai service manual for exact specifications). Test the harness for continuity to the ECM and check for shorts to ground.

Step 3: Voltage Check
With the ignition on and sensor disconnected, measure voltage at the harness connector. You should see approximately 5 volts reference voltage from the ECM. No voltage indicates a harness break or ECM issue.

Step 4: Component Replacement
If the sensor tests out of specification or the harness shows damage, replace the faulty component. For used machines, always apply dielectric grease to connector pins and secure harnesses away from heat sources and moving parts to prevent recurrence.

Step 5: Clear Code and Verify
Use Hyundai diagnostic software (Hi-SDS) or a compatible scan tool to clear the fault code. Run the engine through a full warm-up cycle and monitor for code reappearance.

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Disclaimer: This guide provides general troubleshooting information. For complex electrical diagnostics or if the issue persists, consult a certified Hyundai heavy equipment technician or authorized service center. Improper repairs may void warranties or cause additional damage.