What is Hyundai R335LC-9T Fault Code 100-2?

Fault Code 100-2 on the Hyundai R335LC-9T indicates an Engine Speed Sensor (RPM Sensor) signal abnormality or circuit malfunction. This code is triggered when the Electronic Control Module (ECM) detects an irregular or missing signal from the crankshaft position sensor, which monitors engine rotational speed and timing.

This diagnostic trouble code is critical because the engine speed sensor provides real-time data that the ECM uses to control fuel injection timing, throttle response, and overall engine performance. On the R335LC-9T's Cummins QSB6.7 engine, an inaccurate RPM reading can lead to severe performance degradation, improper fuel delivery, and potential engine protection shutdowns. For used excavators, this code often appears due to sensor wear, contaminated connectors, or damaged wiring harnesses common in machines with high operating hours.

Common Symptoms

When Code 100-2 is active on your Hyundai R335LC-9T, you may experience:

• Engine cranks but fails to start, or starts with excessive cranking time
• Erratic engine idle with noticeable RPM fluctuations or sudden stalling
• Loss of power during operation, especially under load conditions
• Check Engine Light (CEL) illuminated on the instrument cluster
• Engine derate mode activating, limiting maximum RPM to protect the engine

Potential Causes

The most common technical causes for Code 100-2 on used R335LC-9T excavators include:

• Failed or contaminated engine speed sensor (crankshaft position sensor) due to heat exposure or oil saturation
• Damaged sensor wiring harness from rubbing against engine components, particularly near the flywheel housing
• Corroded or loose electrical connectors at the sensor or ECM connections—extremely common in machines operating in wet or marine environments
• Broken or missing sensor mounting hardware causing improper air gap between sensor and reluctor wheel
• ECM internal fault or corrupted calibration files (less common but possible in older units)
• Damaged flywheel reluctor ring with missing or damaged teeth

How to Troubleshoot and Fix Code 100-2

Step 1: Visual Inspection Begin by locating the engine speed sensor on the flywheel housing (driver's side of the Cummins QSB6.7 engine). Inspect the sensor, wiring harness, and connector for physical damage, oil contamination, corrosion, or loose connections. On used excavators, check for harness chafing where wires route near the starter motor.

Step 2: Sensor Resistance Testing Disconnect the sensor connector and use a digital multimeter to check resistance across the sensor terminals. The engine speed sensor should typically read 150-300 ohms (consult your service manual for exact specifications). Readings outside this range indicate sensor failure.

Step 3: Wiring Continuity Check Test continuity from the sensor connector to the ECM harness connector. Check for shorts to ground or open circuits. Measure voltage supply from the ECM (should be approximately 5-8 volts DC with ignition on). Repair or replace damaged wiring as needed.

Step 4: Air Gap Verification If the sensor tests good electrically, verify the air gap between the sensor tip and flywheel reluctor wheel. The proper gap is typically 0.5-1.5mm. Use feeler gauges to measure. Incorrect gaps prevent proper signal generation.

Step 5: ECM Diagnostics Connect Hyundai Hi-MATE diagnostic software or compatible Cummins INSITE software to read live sensor data and verify ECM functionality. Clear codes after repairs and perform a test run.

Disclaimer: This guide provides general troubleshooting information. Always consult the manufacturer's service manual for your specific machine serial number. If you lack proper diagnostic tools or experience with high-voltage electrical systems, consult a certified Hyundai or Cummins technician to avoid safety risks or further damage.