What is Hyundai R500LC-7A Fault Code P191-16?

Fault Code P191-16 on the Hyundai R500LC-7A excavator indicates an Engine Speed/Position Sensor Circuit Low Voltage condition with a moderately severe failure mode indicator (FMI 16). This diagnostic trouble code (DTC) means the Engine Control Module (ECM) is receiving an abnormally low voltage signal from the crankshaft position sensor or camshaft position sensor circuit, preventing accurate engine speed monitoring.

This code is critical because the speed/position sensors provide essential data for fuel injection timing, engine speed control, and overall combustion management. When the ECM cannot accurately read engine RPM or crankshaft position, the R500LC-7A may enter derate mode or experience starting difficulties, directly impacting productivity and potentially causing further engine damage if ignored.

Common Symptoms

• Engine cranks but fails to start or experiences extended cranking times before firing
• Check Engine Light (CEL) or malfunction indicator lamp illuminated on the dashboard
• Loss of engine power or automatic derate to reduced RPM (typically 1200-1500 RPM maximum)
• Rough idle or irregular engine performance, particularly during cold starts
• Intermittent stalling during operation, especially when transitioning between idle and working speeds

Potential Causes

The most common technical causes for P191-16 on used R500LC-7A excavators include:

• Damaged or corroded wiring harness at known rub points near the engine block where the sensor cable routes along the timing cover
• Failed crankshaft position sensor due to heat degradation, oil contamination, or internal coil breakdown (common after 8,000+ operating hours)
• Corroded or loose connector terminals at the sensor plug, particularly from moisture intrusion in harsh operating environments
• ECM internal circuit failure affecting the sensor signal processing (less common but possible in high-hour machines)
• Damaged reluctor ring on the crankshaft or camshaft causing inconsistent magnetic field readings
• Low battery voltage or poor ground connections affecting sensor power supply

How to Troubleshoot and Fix Code P191-16

Step 1: Visual Inspection Begin by inspecting the crankshaft position sensor (located on the lower timing cover, driver's side) and its wiring harness. On used excavators, check for cable chafing where the harness contacts the engine block, oil contamination on connectors, and physical damage to the sensor body. Clean all connector pins with electrical contact cleaner and ensure they're free of corrosion.

Step 2: Electrical Testing Using a digital multimeter, perform resistance checks on the sensor itself (typically 200-1000 ohms depending on sensor type—consult your service manual). Check for continuity in the wiring harness from sensor to ECM. Measure supply voltage at the sensor connector with ignition on (should read approximately 5-12V depending on sensor type). Verify ground circuit integrity with resistance less than 5 ohms.

Step 3: Signal Testing and Component Replacement Connect Hyundai Hi-MATE diagnostic software or compatible CANbus diagnostic tool to monitor live sensor data during cranking. The signal should show consistent pulses corresponding to crankshaft rotation. If voltage remains below 0.5V or shows no fluctuation, replace the speed/position sensor with a genuine Hyundai part. For used machines, always replace the sensor O-ring and apply dielectric grease to connectors during reassembly.

Step 4: Verification After repairs, clear fault codes using diagnostic software, perform a complete engine cycle (cold start to operating temperature), and verify the code does not return. Test under load conditions to ensure proper sensor operation during typical working RPM ranges.

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Disclaimer: This guide provides general troubleshooting information. Always consult the official Hyundai R500LC-7A service manual and consider professional diagnostic assistance for complex electrical issues. Improper repairs may void warranties or cause additional damage.