What is Hyundai R805LC-7 Fault Code 100-2?

Fault Code 100-2 on the Hyundai R805LC-7 excavator indicates an Engine Speed Sensor (ESS) malfunction - specifically a signal abnormality or intermittent connection issue with the crankshaft position sensor circuit. This code is triggered when the Electronic Control Module (ECM) detects irregular or absent pulse signals from the sensor that monitors engine rotational speed and crankshaft position.

This code is critical for the R805LC-7 because the engine speed sensor provides essential real-time data that the ECM uses to control fuel injection timing, engine governor response, and overall performance optimization. When this sensor malfunctions, the machine's ability to maintain proper engine speed under varying loads becomes compromised, directly affecting hydraulic system performance and productivity.

Common Symptoms

• Erratic engine RPM fluctuations during operation, particularly when transitioning between idle and working speeds
• Illuminated engine warning lamp on the instrument cluster, sometimes accompanied by fault code display
• Hard starting conditions or extended cranking time before the engine fires
• Power loss or derate mode activation, where the ECM limits engine output to prevent potential damage
• Intermittent engine stalling at idle or during low-speed hydraulic operations

Potential Causes

The most common causes of Code 100-2 on used R805LC-7 excavators include:

• Worn or damaged engine speed sensor due to heat exposure, vibration, or internal component degradation common in high-hour machines
• Corroded or loose electrical connectors at the sensor harness connection point, especially on machines operated in wet or marine environments
• Wiring harness abrasion or chafing near the engine block or bellhousing area where the harness routing contacts metal surfaces during normal vibration
• Contaminated sensor face from oil leaks, metal debris, or buildup affecting the magnetic pickup gap
• Faulty ECM (less common) with internal circuit board issues in the speed sensor input channel

How to Troubleshoot and Fix Code 100-2

Step 1: Visual Inspection and Connection Check Begin by locating the engine speed sensor on the flywheel housing (typically on the left side of the engine block). Disconnect the sensor connector and inspect for corrosion, bent pins, moisture intrusion, or oil contamination. On used excavators, pay particular attention to connector seal integrity and clean contacts with electrical contact cleaner.

Step 2: Sensor Resistance Testing Using a digital multimeter, measure the sensor's resistance across its two terminals. The reading should typically fall between 500-1500 ohms at room temperature (consult the Hyundai service manual for exact specifications). A reading outside this range indicates sensor failure requiring replacement.

Step 3: Wiring Harness Continuity Check Test continuity from the sensor connector back to the ECM harness connector pins. Check for shorts to ground by measuring resistance between each wire and chassis ground (should read infinite resistance). Inspect the harness routing for friction points against engine components—a common failure point on high-hour R805LC-7 machines.

Step 4: Air Gap Verification If sensor resistance tests normal, remove the sensor and verify the air gap between the sensor tip and flywheel teeth (typically 0.3-1.0mm). Excessive gap from sensor backing out or flywheel wear can cause intermittent signals.

Step 5: Clear Codes and Test After repairs, clear fault codes using Hyundai diagnostic software (Hi-MATE) or a compatible scan tool, then operate the machine under load to verify the repair.

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Disclaimer: This guide provides general troubleshooting information. Always consult the official Hyundai service manual for your specific machine serial number and consider professional diagnostic assistance for complex electrical issues or ECM-related problems.