What is Hyundai HX220 NL EPFC Fault Code 1718 (1322-31)?

Fault Code 1718 (1322-31) indicates a malfunction in the engine coolant temperature sensor circuit, specifically detecting an intermittent or erratic signal from the coolant temperature sensor to the ECM (Engine Control Module). This code is part of the Hyundai excavator's electronic diagnostic system and signals that the ECM is receiving inconsistent voltage readings from the coolant temperature sensor, preventing accurate engine temperature monitoring.

This fault is critical for the HX220 NL EPFC because the coolant temperature sensor directly influences fuel injection timing, engine warm-up cycles, and emission controls. When this sensor malfunctions, the ECM cannot properly regulate engine performance, potentially leading to poor fuel economy, increased emissions, or engine overheating. In used excavators, this code often appears due to age-related wiring degradation or connector corrosion rather than actual sensor failure.

Common Symptoms

• Check engine warning light illuminated on the instrument panel, sometimes flashing intermittently
• Rough idling or hesitation during cold starts, as the ECM defaults to preset temperature values
• Reduced engine power or derate mode activation to protect the engine from potential overheating
• Erratic temperature gauge readings that fluctuate abnormally or show unrealistic values
• Increased fuel consumption due to incorrect fuel mapping based on faulty temperature data

Potential Causes

The most common technical causes for Code 1718 (1322-31) on used Hyundai HX220 excavators include:

• Corroded or loose electrical connectors at the coolant temperature sensor, especially where the harness passes near the engine block
• Damaged wiring harness due to heat exposure, abrasion against engine components, or rodent damage in stored machines
• Failing coolant temperature sensor with internal resistance deterioration common in machines with 5,000+ operating hours
• Intermittent ground connection in the sensor circuit caused by rust or paint on grounding points
• ECM connector pin corrosion affecting signal integrity, particularly in machines operated in humid or coastal environments
• Coolant contamination causing sensor element fouling or incorrect readings

How to Troubleshoot and Fix Code 1718 (1322-31)

Step 1: Visual Inspection Begin by inspecting the coolant temperature sensor located on the engine block near the thermostat housing. Check for physical damage, coolant leaks, or corrosion on the sensor body. Trace the wiring harness from the sensor to the ECM, looking for chafing points, especially where wires contact metal brackets or pass through bulkheads. On used excavators, pay special attention to harness sections exposed to engine heat, as insulation degradation is common.

Step 2: Electrical Testing Using a digital multimeter, disconnect the coolant temperature sensor connector and measure resistance across the sensor terminals. At room temperature (20°C/68°F), resistance should typically read 2,000-3,000 ohms (consult your service manual for exact specifications). Test the wiring harness continuity from the sensor connector to the ECM pins, ensuring readings below 5 ohms. Check for voltage supply from the ECM (typically 5 volts reference) with the ignition on.

Step 3: Connector and Ground Verification Inspect all connector pins for corrosion, bent terminals, or moisture intrusion—common issues in older machines. Clean connectors with electrical contact cleaner and apply dielectric grease. Verify the sensor ground circuit by measuring resistance to chassis ground (should be less than 1 ohm). For used excavators, remove and clean the grounding point, ensuring bare metal contact.

Step 4: Component Replacement and Verification If testing reveals sensor resistance outside specifications or intermittent readings, replace the coolant temperature sensor with a genuine Hyundai or OEM-equivalent part. After replacement, clear the fault code using Hyundai diagnostic software (Hi-MATE or compatible scan tool) and perform a test cycle. Monitor live data to confirm stable temperature readings that correspond with actual engine temperature.

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Disclaimer: This guide provides general troubleshooting information for experienced technicians. Always consult the official Hyundai service manual for your specific machine serial number. If you're uncomfortable performing electrical diagnostics or working with engine management systems, contact a certified Hyundai heavy equipment technician to prevent misdiagnosis or additional damage.