What is Hyundai HX220 NL EPFC Fault Code 687 (103-18)?

Fault Code 687 (103-18) indicates an Engine Speed Sensor (ESS) circuit malfunction or erratic signal detected by the Electronic Control Module (ECM). This code specifically flags abnormal voltage patterns, intermittent signals, or complete signal loss from the crankshaft position sensor that monitors engine RPM on the Hyundai HX220 NL EPFC excavator.

This fault is critical because the engine speed sensor provides real-time data to the ECM for fuel injection timing, governor control, and engine protection protocols. When this sensor fails or sends inconsistent signals, the excavator's performance becomes unpredictable, potentially causing sudden power loss or preventing the machine from starting altogether. On used excavators, this code often appears due to sensor degradation, wiring harness damage from heat exposure near the flywheel housing, or corrosion in connectors subjected to years of moisture and vibration.

Common Symptoms

• Engine cranks but fails to start or experiences extended cranking time before ignition
• Intermittent engine stalling during operation, especially under load or at idle
• Erratic RPM display on the instrument cluster or complete loss of tachometer reading
• Loss of engine power or activation of derate mode, limiting machine performance to protect the engine
• Check Engine Light (CEL) or malfunction indicator lamp illuminated on the dashboard

Potential Causes

The most common technical causes for Code 687 (103-18) on used HX220 NL excavators include:

• Failed engine speed sensor due to internal component degradation, heat damage, or bearing material contamination on the sensor tip
• Damaged wiring harness between the sensor and ECM, particularly at flex points near the engine mount or along the frame rail where abrasion occurs
• Corroded or loose electrical connectors at the sensor plug or ECM interface, common in machines with high hour counts or exposure to wet conditions
• Damaged flywheel ring gear teeth or excessive air gap between the sensor and reluctor wheel, preventing proper magnetic field generation
• ECM power supply issues or internal ECM faults affecting the sensor circuit's 5-volt or 8-volt reference signal

How to Troubleshoot and Fix Code 687 (103-18)

Step 1: Visual Inspection and Connector Check Begin by locating the engine speed sensor on the flywheel housing (typically passenger side, lower engine block). Inspect the sensor connector for corrosion, bent pins, or moisture intrusion. On used excavators, carefully check the wiring harness routing for signs of rubbing against the engine block, heat damage from exhaust components, or previous repair attempts with electrical tape.

Step 2: Sensor Air Gap and Physical Condition Remove the sensor and inspect the tip for metal debris, cracks, or damage. Measure the air gap between the sensor and flywheel teeth using feeler gauges—specifications typically range from 0.5mm to 1.5mm (consult service manual). Check flywheel teeth for damage, cracks, or missing segments that could cause erratic signals.

Step 3: Electrical Testing with Multimeter Using a digital multimeter (DMM), perform resistance checks on the sensor terminals. A functional engine speed sensor typically measures between 200-1000 ohms (verify exact specification in Hyundai service literature). Check for short circuits to ground by measuring resistance between each sensor terminal and the engine block—readings should show infinite resistance (open circuit).

Step 4: Dynamic Signal Testing With the sensor reconnected and using Hyundai Hi-Mate diagnostic software or compatible scan tool, monitor live sensor data while cranking the engine. The ECM should receive an AC voltage signal (typically 0.5-5 volts AC) that fluctuates with crankshaft rotation. Inconsistent signals, dropouts, or complete absence confirms sensor or wiring failure.

Step 5: Harness Continuity and ECM Verification Disconnect both the sensor and ECM connectors. Test continuity through the harness wires—readings should show less than 5 ohms resistance. Check for cross-circuit shorts between signal wires. If harness and sensor test properly but the code persists, the ECM sensor input circuit may require professional diagnosis or ECM replacement.

Critical for Used Excavators: Before replacing components, thoroughly clean all connectors with electrical contact cleaner and apply dielectric grease to prevent future corrosion. Many apparent sensor failures on high-hour machines are actually connection issues that resolve with proper maintenance.

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Disclaimer: This guide provides general troubleshooting procedures for informational purposes. Always consult the official Hyundai service manual for your specific machine serial number and software version. If you lack proper diagnostic tools or experience with high-voltage electrical systems, consult a certified Hyundai heavy equipment technician to prevent injury or further machine damage.