What is Hyundai HX220 NL EPFC Fault Code 197 (111-18)?

Fault Code 197 (111-18) indicates an Engine Coolant Temperature (ECT) sensor circuit malfunction—specifically a high voltage condition detected by the Engine Control Module (ECM). This code triggers when the ECM receives a voltage signal from the ECT sensor that exceeds the normal operating range, typically above 4.5-4.8 volts, suggesting an open circuit, damaged sensor, or wiring issue.

On the Hyundai HX220 NL EPFC excavator, the ECT sensor plays a critical role in monitoring engine operating temperature and adjusting fuel injection timing, idle speed, and cooling fan operation. When this sensor circuit fails, the ECM cannot accurately regulate engine performance, potentially leading to overheating, increased emissions, and reduced fuel efficiency. For used excavators, this code often signals age-related deterioration of electrical components rather than catastrophic engine failure.

Common Symptoms

• Engine warning lamp illuminated on the instrument cluster with reduced power output
• Hard starting conditions, especially during cold weather, as the ECM defaults to predetermined temperature values
• Erratic cooling fan operation—fans may run continuously or fail to activate when needed
• Black smoke from exhaust due to improper fuel mixture calculations based on faulty temperature data
• Rough idle or stalling when the engine is cold, as fuel delivery isn't optimized for actual temperature

Potential Causes

The most common technical causes for Code 197 (111-18) on used HX220 excavators include:

• Open circuit in ECT sensor wiring harness—particularly where the harness routes near the engine block or exhaust manifold, common wear points on machines with 5,000+ hours
• Failed ECT sensor with internal resistance breakdown, typical after prolonged heat cycling
• Corroded or loose connector terminals at the sensor or ECM connection points due to coolant leaks or moisture intrusion
• Damaged ECM pin connections from vibration stress over years of operation
• Broken or frayed wires inside the protective loom, often invisible without physical inspection

How to Troubleshoot and Fix Code 197 (111-18)

Step 1: Visual Inspection Begin by locating the ECT sensor on the engine block (typically near the thermostat housing). Inspect the sensor connector and wiring harness for obvious damage—look for corroded pins, coolant residue, cracked insulation, or chafed wires rubbing against engine components. On used excavators, pay special attention to harness routing near vibration points.

Step 2: Sensor Resistance Testing Disconnect the ECT sensor connector 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 your service manual for exact specifications). If readings show infinite resistance (open circuit) or zero resistance (short circuit), replace the sensor.

Step 3: Circuit Voltage Check With the sensor disconnected and ignition on (engine off), measure voltage at the harness connector (machine side). You should see approximately 5 volts reference voltage from the ECM. If voltage is absent or incorrect, trace the wiring back to the ECM, checking for breaks or shorts to ground.

Step 4: Connector and Harness Repair For used machines, thoroughly clean all connector terminals with electrical contact cleaner and apply dielectric grease. Repair any damaged wiring using heat-shrink solder connections—never use crimp connectors in high-vibration environments. Re-route harnesses away from heat sources and secure with proper clips.

Step 5: Clear Code and Test After repairs, clear the fault code using Hyundai diagnostic software (Hi-MATE) or a compatible scan tool. Operate the machine through a complete heat cycle, monitoring coolant temperature readings to ensure they match actual engine conditions.

---

Disclaimer: This guide provides general troubleshooting information. Always consult the Hyundai HX220 service manual for model-specific procedures and torque specifications. If you're uncomfortable performing electrical diagnostics, contact a certified Hyundai heavy equipment technician to prevent further damage to the ECM or wiring harness.