What is Hyundai R805LC-7 Fault Code 111-2?

Fault Code 111-2 on the Hyundai R805LC-7 excavator indicates an Engine Speed Sensor (RPM Sensor) circuit malfunction, specifically a low voltage or intermittent signal condition. This code triggers when the Engine Control Module (ECM) detects an abnormal voltage reading from the engine speed sensor, which monitors crankshaft rotation and provides critical data for fuel injection timing, governor control, and overall engine performance.

The engine speed sensor is fundamental to the R805LC-7's Cummins QSX15 engine operation. Without accurate RPM data, the ECM cannot properly regulate fuel delivery, manage turbocharger boost, or coordinate auxiliary systems. In used excavators, this sensor circuit is particularly vulnerable to wear from heat cycling, vibration, and exposure to moisture around the engine block mounting location.

Common Symptoms

When fault code 111-2 is active on your Hyundai R805LC-7, operators typically experience:

• Engine warning light illuminated on the instrument cluster with possible engine derate mode activation
• Rough idling or unstable engine speed, particularly at low RPMs during warm-up
• Intermittent engine stalling when transitioning from idle to working loads
• Loss of power under heavy hydraulic demand, as the ECM defaults to conservative fuel mapping
• Difficulty starting the engine, especially when hot, due to incorrect timing signals

Potential Causes

Several technical failures trigger this fault code in used R805LC-7 excavators:

• Magnetic pickup sensor failure from heat degradation or internal coil breakdown (common after 8,000+ operating hours)
• Damaged sensor wiring harness at rub points near the engine mounting brackets or starter motor
• Corroded or loose connector pins at the 3-pin sensor connector, allowing moisture intrusion
• Crankshaft reluctor ring damage (missing teeth or metallic debris buildup affecting sensor gap)
• ECM internal circuit malfunction in the sensor input module (rare but documented in high-hour machines)
• Poor ground connection at the engine block ground strap, causing voltage reference drift

How to Troubleshoot and Fix Code 111-2

Step 1: Visual Inspection and Connector Check Begin by locating the engine speed sensor on the left side of the engine block, near the flywheel housing. Inspect the wiring harness for abrasion points where it contacts metal surfaces—this is a known wear area on R805LC-7 models. Disconnect the 3-pin connector and examine pins for corrosion, bent contacts, or moisture. Clean with electrical contact cleaner and apply dielectric grease.

Step 2: Sensor Resistance and Gap Measurement Using a digital multimeter, measure sensor resistance across the two signal pins (typically 200-1,000 ohms for magnetic pickup sensors; consult Hyundai service manual for exact specification). Check the air gap between the sensor tip and reluctor ring using a feeler gauge—it should be 0.020-0.040 inches. Excessive gap indicates sensor backing out or reluctor ring wear.

Step 3: Dynamic Voltage Testing With the sensor reconnected, use a multimeter set to AC voltage and crank the engine. The sensor should produce a minimum 1.5-2.0 volts AC during cranking. Low or zero voltage confirms sensor failure. For used excavators, also inspect the reluctor ring through the sensor hole with a borescope for missing teeth or metal shavings.

Step 4: Wiring Continuity and ECM Check Test continuity from the sensor connector to the ECM pins using the machine's wiring diagram. Check for opens or shorts to ground. Verify ECM power supply (typically 8-12 volts DC) at the sensor connector. If all wiring tests pass but the code persists, ECM replacement may be necessary, though this is uncommon.

Professional Disclaimer: While these diagnostic steps are standard practice, excavator electrical systems involve high-pressure fuel systems and critical engine controls. Always consult Hyundai service documentation or a certified heavy equipment technician for used machinery with unknown maintenance history.