What is Hyundai R805LC-7 Fault Code P191-16?

Fault Code P191-16 indicates an abnormal voltage condition in the Engine Speed/Position Sensor Circuit on the Hyundai R805LC-7 excavator. This Diagnostic Trouble Code (DTC) is triggered when the Electronic Control Module (ECM) detects that the crankshaft position sensor or camshaft position sensor is sending erratic or out-of-range voltage signals beyond the manufacturer's specified parameters.

This code directly affects the ECM's ability to accurately monitor engine timing and calculate proper fuel injection sequences. For the Cummins QSX15 or similar engines equipped in the R805LC-7, this sensor data is absolutely critical for maintaining optimal combustion timing, fuel efficiency, and emissions compliance. When the ECM cannot reliably read engine position, it may default to limp mode or restrict performance to prevent catastrophic engine damage.

Common Symptoms

When P191-16 is active on your R805LC-7, operators typically experience:

• Engine Warning Light illuminated on the instrument cluster with possible derate notification
• Hard starting conditions or extended cranking time, especially when the engine is cold
• Rough idling or intermittent engine stalling during low-load operations
• Loss of power or automatic derate mode limiting engine RPM to 1200-1500 range
• Erratic tachometer readings or complete tachometer failure during operation

Potential Causes

The most common technical causes for P191-16 on used R805LC-7 excavators include:

• Worn or damaged crankshaft/camshaft position sensor due to age, heat exposure, or internal component failure
• Corroded or damaged wiring harness at connector points, particularly where harnesses pass near the engine block or exhaust components
• Intermittent short circuits caused by harness abrasion against frame rails or hydraulic lines—a known issue on high-hour R805LC-7 machines
• Contaminated sensor face from oil leaks, metal debris, or excessive carbon buildup affecting magnetic pickup
• Faulty ECM or corrupted ECM software calibration (less common but possible on machines with 8,000+ hours)
• Poor ground connections at sensor mounting points or ECM ground straps

How to Troubleshoot and Fix Code P191-16

Step 1: Visual Inspection and Connector Assessment

Begin by locating the crankshaft position sensor (typically mounted on the lower engine block near the flywheel housing) and camshaft position sensor (usually on the timing case cover). Inspect both sensor connectors for corrosion, bent pins, or moisture intrusion. On used excavators, pay special attention to connector seals—these often deteriorate after 5-7 years, allowing water contamination. Clean connectors with electrical contact cleaner and apply dielectric grease.

Step 2: Sensor Resistance and Voltage Testing

Using a digital multimeter, disconnect the sensor connector and measure resistance across the sensor terminals. Most position sensors on this platform should read between 200-1,000 ohms at room temperature (consult the Hyundai service manual for exact specifications). Next, reconnect the sensor and perform a back-probe voltage test while cranking the engine—you should see an AC voltage signal fluctuating between 0.5-5.0 volts. Irregular or absent voltage indicates sensor failure.

Step 3: Harness Continuity and Short Circuit Testing

Disconnect both ends of the sensor harness (at sensor and ECM). Check for continuity between each wire from sensor connector to ECM connector—resistance should be less than 5 ohms. Test each wire against chassis ground; any reading below infinite resistance indicates a short circuit. For used R805LC-7 excavators, physically trace the harness routing, looking for wear points where cables contact the engine, frame, or hydraulic components—these machines are notorious for harness chafing near the engine mount brackets.

Step 4: Sensor Air Gap and Mounting Verification

If electrical tests pass, remove the position sensor and inspect the reluctor ring or tone wheel it reads from. Look for missing teeth, excessive runout, or metal debris accumulation. Verify the air gap specification (typically 0.5-1.5mm) using a feeler gauge when reinstalling. On high-hour machines, worn engine mounts can cause misalignment affecting sensor reading accuracy.

Step 5: ECM Evaluation and Software Check

If all physical components test correctly, connect Hyundai Hi-MATE diagnostic software or an equivalent J1939-compatible scan tool. Clear the code and monitor live sensor data during operation. Erratic signal patterns despite good sensor readings may indicate ECM input circuit failure. Check for available ECM software updates—Hyundai released calibration updates for 2010-2013 R805LC-7 models addressing sensor interpretation algorithms.

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Professional Disclaimer: While these troubleshooting steps are comprehensive, complex electrical diagnostics on electronically-controlled excavators require proper training and equipment. Always consult the official Hyundai service manual for your machine's specific serial number range, and consider engaging a certified Hyundai technician for ECM programming or advanced diagnostics. Improper repairs can result in additional ECM damage or safety hazards.